Kinetics Worksheets Questions

 

 

Power Point Lesson Notes- double click on the lesson number.                              

 


Worksheet Answers             Quiz Answers

 

1          Monitoring Reaction Rates                              WS 1                                       Q1

2          Factors that Change the Rate                           WS 2                                       Q2

3          Collision Theory                                             WS 3                                       Q3

4          PE Diagrams                                                   WS 4                                       Q4

5          Mechanisms                                                    WS5                                        Q5                                                                              

6          Lab: The Iodine Clock Reaction                     Web Review                                 Lab Handout

7          Review                                                            Practice Test 1                   Practice Test 2

8.         Review                                                            Quizmebc

9.         Test

 

 

Text book        Hebden     Read  Unit I

 

 

 

            The following workbook is designed to ensure that you can demonstrate your understanding of all aspects of the kinetics unit. The minimum expectation is that you do all of these questions by the due dates given by your teacher. Do the questions. Use your notes from class to assist you. Then after you have finished go to the web site to evaluate your work. Make a list of those things that you dont quite understand and bring them to class. I will go over them as best as I can. There are other things that you should do to prepare for the test at the end of the unit. Remember, what you put into this course is what you will get out. There is no substitute for consistent effort and hard work. If you cant do a question, get some help before the end of the unit, you need to know, understand, and remember everything. Good luck! I know you can do well in this unit. Web Site Address:  iannonechem.com

 

 

 

Ws #1              Monitoring and Calculating Reaction Rates

 

1. Read unit 1 of Hebden over the next week. A students should read it twice.

2. a) When measuring a property associated with a reactant in a reaction, does it increase or decrease?

            Decrease as reactants are converted into products                       

2. b) When measuring a property associated with a product in a reaction, does it increase or decrease?                               

            Increase as reactants are converted into products

3. Give three ways to measure the rate of the following reaction. State the specific properties that you would monitor and include units (amount is not a specific property). State if each property would increase or decrease. Describe in each case how you would calculate the reaction rate.

 

2HNO3(aq)        +     Cu(s)      NO2(g) +H2O(l) + CuNO3(aq)

The first one is done for you.

 

i)          Mass of Cu                                         Grams                         Decrease                               Rate = mass/time

ii)         [HNO3]                                               M                                Decrease                                Rate = M/time

iii)        Volume of NO2                                            L                                 Increase                                 Rate = L/time

iv)        [CuNO3]                                             M                                increase                                  Rate = M/time

v)         Mass of open container                     Grams                         Decrease                                Rate = mass/time

vi)        Pressure of closed container             KPa                             Increase                                 Rate = Pressure/time

 

Any three of the above answers are fine.

           

Mass of copper (g)                  3.26                             2.93                                         2.61

Time (min)                              5.0                               7.0                                           9.0                                                                                          

                       

           

4. Calculate the rate in units of (g Cu/min).

3.26  - 2.61 g Cu    = 0.16g/min

    9.0 - 5.0 min

 

5. Calculate the rate in units of (mole Cu/min).

0. 16g Cu  x       1 mol   = 0.0026 mol/min

    min                 63.5 g          

 

6. Calculate the rate in moles HNO3 consumed per second (remember that 2 moles are consumed per 1 mole of Cu).

0.0026 mol Cu      x    1 min      x       2 moles HNO3  =  8.5 x 10-5 moles/s

       min                       60s                    1 mole Cu

 

7.  Calculate the rate in units of (g/sec) for HNO3.

8.5 x 10-5 moles HNO3   x   63.0 g      = 0.0054 g/s

            s                               1 mole

 

 

                                                                                                                                                          

            Volume of NO2 (mL)                           10.0                 11.5                 12.7

            Time (sec)                                           0.00                 5.00                 10.00

 

8.  Calculate the rate in units of (mL NO2/sec).

Rate = 12.7 - 10.0 ml   = 0.27 ml/s

            10.00 - 0.00 s

9. Calculate the rate in units of (L NO2/min).

0.27 ml   x   60s   x   1L         = 0.016 L/min

     s             1 min    1000 ml

 

10. Calculate the rate in units of (moles NO2/min) at STP.

0.0162 L   x   1 mol   = 7.2 x 10-4 mol/min

  min              22.4 L

 

11. Calculate the rate in units of (moles HNO3/min) at STP (remember that 2 moles are consumed per 1 mole of NO2)

7.23 x 10-4 mol NO2   x   2 moles HNO3   = 0.0015 moles/min

            min                      1 mole NO2

 

12. Calculate the rate of the following reaction:

           

 

            2NO (g)    +     2H2 (g)        N2 (g)  +    2H2O (g)

 

 

                 
 

           

                        Rate    =          (0.080 0.020) moles             =          0.0060 moles/s           

                                                (12.0 2.0) s

 

a) What is the rate in moles NO per second?                          0.0060 moles/s

b) What is the rate in moles N2 per second?                            0.0030 moles/s

c) What is the rate in grams NO per min?                               11 g/min

d) What is the rate in grams N2 per hour?                                3.0 x 102g/h

 

13. Choose three properties that you could measure in order to monitor the rate of the following reaction.

Cu (s)   +   2AgNO3 (aq)       2 Ag (s)    +  Cu(NO3)2 (aq)

 

            Property                                  Unit of Measurement                                       Change

 

1.          Mass Cu                                  grams                                                            decrease           

 

2.         Mass Ag                                   grams                                                             increase           

 

3.         Intensity [Cu+2]                        M                                                                  increase           

 

14. Calculate the rate of the following reaction in units of M/s:

 

Zn (s)  +  2HCL (aq)      ZnCl2 (aq)    +     H2 (g)

 

Molarity of HCL (M)              0.612               0.813               1.05

time (seconds)                         21.0                 25.0                 29.0

 

 

Rate =  (1.05 - 0.612) M        =          0.055 M/s

               (29.0 - 21.0) s

 

 

15. Calculate the rate of the following reaction in L/min:

 

Zn (s)  +  2HCL (aq)      ZnCl2 (aq)    +     H2 (g)

 

Volume of H2   (L)                   0.255               0.550               0.790

 

time (minutes)                         1.0                   2.0                   3.0

 

 

Rate =  (0.790 - 0.255) M      =          0.27 L/min

                  (3.0 - 1.0) s

 

 

16. If 0.369g of HCl is neutralized with 0.250M NaOH in 25.0 seconds, what is the reaction rate in moles HCL /min.

 

 

 

                                    0.369g   x   1 mole

            Rate =                                 36.5g       = 0.0243 mole/min

                                  0.41666 min

                                                                                 

                         

 

WS # 2                      Factors That Change The Reaction Rate

 

Homogeneous reactions

- reactants are in the same phase (aq), (g) , or (l) and are thoroughly mixed.

Heterogeneous reactions

- reactants are in the two or more phases and are not thoroughly mixed (two solids do not mix).

 

Classify as Homogeneous or Heterogeneous:

 

1.                   Zn (s)  +  2 HCl (aq)             H2 (g)  +  ZnCl2  (aq)        heterogeneous                                                                                                                                                        

  2.                   Ag+ (aq)  +  Cl- (aq)                AgCl  (s)                                       homogeneous                       

                                         

3.                   H2 (g)    +  F2 (g)                     2HF (g)                                          homogeneous          

 

4.                   2Al (s)  +  3I2 (s)                   2AlI3  (s)                                       heterogeneous                     

 

 

The following four factors will increase the rate of a chemical reaction that is homogeneous:

         

         1.          Increasing the temperature.                                                            

         2.          Increasing the reactant concentration.                                                       

         3.          Adding a catalyst                                                                  

         4.          Changing the nature of the reaction.

         5.          Increasing the pressure for gases                                                    

 

The above four factors as well as the two below will increase the rate of a heterogeneous reaction:

        

         6.          Increasing the surface area of a solid.                                                        

         7.          Agitation       

 

Which factor will only increase the rate of a gaseous reaction?                   

 

         8.          Pressure                                            

 

For each reaction specifically describe all of the ways to increase the reaction rate 

(i.e.. increase[H2]).

1.      H2 (g)    +  F2 (g)        2 HF (g)         This reaction is homogeneous so the first four factors will work.

 

         Increasing the temperature

         Increasing the pressure

         Increasing [H2] or [F2]

         Adding a catalyst

 

 

2.      HCl (aq)  +  NaOH (aq) → NaCl (aq)  +  H2O  (l)        This reaction is homogeneous so the first four factors will work.

 

         Increasing the temperature

         Increasing [HCl] or [NaOH]

         Adding a catalyst

        

3.         Zn (s)  +  2 HCl (aq)         H2 (g)  +  ZnCl2  (aq)    This reaction is heterogeneous most of the factors will work, except pressure- need a gaseous                                                                             reactant..

 

         Increasing the temperature

         Increasing [HCl]

         Adding a catalyst

         Increasing the surface area of Zn(s)

         Agitation

 

4.      State three examples of chemical reactions that are desired to be slow.

 

            Food spoiling

            Metal corrosion

            Erosion

           

           

 

5.      Give three examples of chemical reactions that are desired to be fast.

 

         Combustion of gasoline in automobiles

         Industrial chemical production

         Cooking food

         The combustion of gasoline in a car engine; while accelerating.

 

 

6.      List all of the ways to increase the rate of the following reaction:

                      H2O2 (aq) H2 (g)    +  O2 (g)

 

         Increasing the temperature

         Increasing [H2O2]

         Adding a catalyst

 

 

I. Homogeneous reactions are generally faster than heterogeneous- the reactants are mixed better and therefore there are more collisions between reactant particles.

 

 HCl (aq)  +  NaOH (aq)          NaCl (aq)  +  H2O  (l)    

 

is    faster than

 

Zn (s)  +  2 HCl (aq)         H2 (g)  +  ZnCl2  (aq)

 

II.  Simple ionic reactions (where there are no bonds to break) are generally faster than more complex ionic reactions (where there are bonds to break).

 

Pb+2 (aq)  +  2Cl- (aq)                 PbCl2  (l)    

 

is    faster than

 

2Na+ (aq)  +  2ClO- (aq)           2Na+ (aq)   +  2Cl-(aq)        +     O2  (g)

 

 

1. Indicate the faster and slower reaction and explain why.

 

a) 2Al (s)  +  3I2 (s)                           2AlI3  (s)

 

            Heterogeneous reaction with bonds to break will be slow.                                                                                                                                   

 

b) Ag+(aq)    +   Cl-(aq)           AgCl (s)

 

            Homogeneous reaction with no bonds to break will be fast.                                                                                                                                             

2. Indicate the faster and slower reaction and explain why.

 

a) 2Al (s)  +  3I2 (s)                           2AlI3  (s)

 

            Slow. The reaction is heterogeneous (two solid do not mix) with bonds to break.                                                                                                                                                           

 

b) 2Na+ (aq)  +  2ClO- (aq)                        2Na+ (aq)   +  2Cl-(aq)        +     O2  (g)

 

                                                                                                                                                           

            Faster. The reaction is homogeneous.

 

 

3. Indicate the faster and slower reaction and explain why.

 

a) 3Ba+2(aq)    +    2PO4-3 (aq)        Ba3(PO4)2(aq)

 

            Faster. The reaction is homogeneous and simple ionic with no bonds to break.                                                                                                                                      

 

b) Cu(s)   +  2Ag+(aq)       Cu+2 (aq)    +    2Ag (s)

 

            Slow. The reaction is heterogeneous and the Cu(s) bonds need to be broken.                                                                                                                              

 

Ws # 3 Collision Theory

 

1.     Chemical reactions are the result of collisions between reactant particles, where bonds are broken and new ones form.

2.     A successful collision requires sufficient energy and favorable geometry.

3.     Describe as fast, medium or slow. Explain!

       

        i) 2 H2 (g) + O2 (g)        2 H20 (l)  (room temperature)

           

            Slow. Gas reactions are slower than aqueous.

 

        ii) 2 Ag+ (aq) + CO32- (aq)    → Ag2CO3  (s)

           

            Fast. Homogeneous reaction simple ionic- there are no bonds to break

 

        iii)           2 HCl (aq) + Na2CO3 (aq)                  CO2 (g) + 2 NaCl (aq) + H20 (l)

           

            Medium. Homogeneous complex reaction - there are bonds to break.

 

4.     i) Describe how you would measure the rate of the reaction :

           

            Zn (s) + 2 HCl (aq)                  ZnCl2 (aq)   + H2 (g)

           

            Measure the decrease in Zn mass.

            Measure the increase in H2 gas volume.

            Measure the mass of an open container which decreasing due H2 escaping.

 

        ii) List four ways to increase the rate.

                     

                      Increasing the temperature

                      Increasing [HCl]

                      Adding a catalyst

                      Increasing the surface area of Zn(s)

                        Agitation

 

5.     A 10 C temperature increase frequently doubles the rate of a slow reaction because:

            a) The temperature has doubled.

            b) The PE of the colliding particle has doubled.

            c) The KE of the colliding particle has doubled.

            d) The fraction of particles with sufficient KE to react has doubled.

 

 

 

 

6.     Both collisions A and B have the same KE. Which collision is successful and explain why.

                     Before Collision                        After Collision

 


        A)


 

 

 

 


 



        B)

 

 


           

        Collision B was successful due to favourable geometry.

 

 

7.     Use the collision theory to explain how each factor increases the reaction rate.

        i)  Increasing temperature                                                i)         more collisions and harder collisions

        ii) Increasing [reactants]                                                  ii)        more collisions

        iii)           Increasing surface area (solid)                        iii)       more collisions

        iv)            Agitation of a heterogeneous reaction             iv)       more collisions          

        v)             Adding a catalyst                                             v)         lower Ea & low energy collisions are successful

           

8.     Explain why collision A was successful while collision B was unsuccessful.

                     Before Collision                                                            After Collision

 


        A)           


 

 

 

 


 


        B)

 

 

           

            Collision A was successful because it had sufficient energy. The geometry is the same for both collisions.

 

 

 

Explain each of the following using the collision theory. You need to explain each statement.

 

9.

       a candle is not burning at room temperature                      Ea is too high

       a match lights the candle                                                   Provides Ea

       the candle continues to burn                                              Exothermic

 

10.

       H2O2 decomposes slowly at 20o C                                    Ea is too high

       KI is added and rapid decomposition begins                    Catalyst- lowers Ea

       The temperature increases                                                 Exothermic

 

11.

       H2 and O2 in a balloon do not react                                   Ea is too high

       A spark ignites the balloon                                                Provides Ea

       An explosion results                                                          Exothermic

12.

       CH4 and O2 in a balloon do not react                                Ea is too high

       A platinum gauze ignites the balloon                                 Catalyst lowers Ea

       An explosion results                                                          Exothermic

 

13. N2(g)  +   O2(g)         2NO(g)

 

Even though there are more than four billion collisions per second between N and O the amount of product after a year is too small to detect. Using the collision theory, give two reasons why this reaction might be slow.

i)         Low Temperature                                                                                                                                                    

ii)        High Ea                                                                                                                                                         

 

14. Give two reasons why some collisions will not result in a chemical reaction.

 

i)         Insufficient energy                                                                                                                                                   

ii)        Poor geometry                                                                                                                                                          

 

15. Give five reasons that might account for the following reaction having a high rate.

Ca (s) + 2 HCl (aq)     CaCl2 (aq)   + H2 (g)

 

i)         High surface area of Ca                                                                                           

ii)        High concentration of HCl                                                                                       

iii)       High temperature                                                                                         

iv)       Agitation                                                                                           

v)         Nature of the reactant                                                                                             

 

 

16. C(s)   +    O2(g)      CO2(g)

List four ways the rate of the reaction could be increased.

 

i)         Increase temperature                                                                                               

ii)        Increase [ O2 ]                                                                                               

iii)       Increase pressure                                                                                         

iv)       Increase SA of C                                                                                          

(add catalyst or agitate)

 

17. State the relationship between Activation energy and the rate of a reaction. Graph the relationship.

 

Inverse because decreasing the activation energy increases the rate.

 

 


 


Rate

 

 

 

 

 

 

                  Activation Energy

 

18. State the relationship between Temperature and the rate of a reaction. Graph the relationship.

 

Direct, because increasing the temperature increases the rate.                                       


 

 


Rate

 

 

 

 

 

                  Temperature

 

 

19. State the relationship between Concentration and the rate of a reaction. Graph the relationship.

 

Direct, because increasing the concentration increases the rate.                                     


 


Rate

 

 

 

20.       Give three examples of reactions that are desired to be slow.

            a)         food spoiling

            b)         corrosion of metal

            c)         the fading of  the colour in paint

 

21.       Give three examples of reactions that are desired to be fast.

            a)         explosions

            b)         the combustion of gasoline in your car when you are passing someone on the freeway

            c)         the commercial production of chemicals

 

 

                 Molarity

 

       

 

22.   List all of the ways to increase the rate of the reaction:

             

        2 H2O2 (aq)         2 H2O (l)  + O2 (g)

 

        Increase the H2O2 concentration

 

        Increase the Temperature

 

        Add KI catalyst

 

23.   Describe how you would measure the rate of the reaction above. State the property you would measure and describe how it changes. Draw a diagram to illustrate your answer.


 


        Mass of an open container        Decreases      

 

 

        or

 

       

        Volume of O2      See notes for diagram.

 

       

 

        Pressure of O2 in a closed system.        See notes for diagram.

 

 

24.       Pick the fastest and the slowest reaction at 20 C.

       

Slowest gases are slower than aqueous                        a)  H2(g)  +  I2(g)            2 HI(g)

                                                                                                b)  2 HCl(aq)   +   Na2CO3(aq)                   CO2(g)  +  2 NaCl(aq)  +  H2O(l)

        Fastest- simple ionic or double replacement                c)   Hg2+(aq)   +   2 I -(aq)                   HgI2(s)

 

 

 

 

25.   H2 and O2 can exist at 20 C for years without reacting. But when a small spark ignites the mixture it reacts explosively. Explain using the Collision Theory.

 

            The activation energy is too high at room temperature so there are no successful collisions.

 

            A spark provides the kinetic energy required to overcome the Ea.

 

            Exothermic reactions produce energy.

 

 

26.       Draw a collision energy distribution diagram for a reaction where the y-axis is fraction of collisions and the x-axis is collision energy. Draw the Ea line showing about 10% of the collisions having sufficient energy. Draw the Ea line for the catalyzed reaction where 20% have sufficient energy.

 


 

 

 

 

 

 

 

 

 


27.       Shade in the area of the collision energy distribution diagram showing those collisions that do not have the required energy to be successful at the temperature below.

 


 

 

 

 

 

 

 

 

 

 

 

28.       Shade in the area of the collision energy distribution diagram showing those collisions that do have the required energy to be successful at the temperature below. Redraw the curve at a higher temperature.


 

 

 

 

 

 

 

 

Collision Energy

 
 

 

 

 

 

 

 

 


Kinetics - Descriptions

 

 

 

Use the collision theory to explain the following. Each sentence must be explained with a statement from the collision theory.

 

1. An unlit candle does not burn. It burns after being lit with a match. It continues to burn.

 

      Ea is too high.

      Match is energy and provides Ea.                                                                                                                                                               

      Exothermic

                                                                                                           

2. A solution is reacting very slowly to produce bubbles. KI is added and although it is not consumed in the reaction , it speeds up the reaction rate. The temperature increases. The rate increases even more.

 

      Ea is high                                                                                                                                                       

      KI is a catalyst and lowers Ea and more collision are successful.

      Exothermic→ temperature increases → rate increases                                                                                                                                                                                                                                                                                 

 

3. Iron reacts slowly with HCl. Iron is replaced with Zn and a much more vigorous reaction rate occurs.

 

      Nature of reactant                       Fe                high Ea                                                                                                                                                                                               Zn               low Ea                                                                                                                                                      

 

4. H2 and O2 can exist together for years at room temperature without reacting. A spark begins the reaction. An explosion results.

 

      High Ea   → collisions are not successful                                                                                                                                                                

      A spark provides the Ea

      Exothermic → explosion                                    

 

                                                                                                                                                     

5. Dilute nitric acid shows little reaction with copper. Concentrated nitric acid vigorously reacts.

 

      Low concentration → few collisions                                                                                                                                                           

      High concentration → many collisions

                                                                                                                       

6. Water puts out a fire.

     

      Lowers temperature so there are less collisions

      The collisions have less energy.                                                                                                                                                       

 

7. Paint prevents rusting.        

 

      There are fewer collisions between reactant molecules.                                                                                                                                                               

8. A preservative in food slows rotting.

 

      The preservative is an inhibitor; which increases the Ea.

                                                                                                                                   

Ws # 4             Potential Energy Diagrams Worksheet

 

1.     Draw the PE diagram showing the PE changes that occur during a successful collision of the exothermic reaction:

 

                        H2    +    I2               2 HI   +  250 KJ

 

        The PE of the reactants = 400 KJ

        The activation energy of the forward reaction =  200 KJ

 

       


Reaction path

 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


2.     Draw the PE diagram showing the PE changes that occur during a successful collision of the endothermic reaction:

 

                        A   +   B   +   200 KJ          C

 

        The PE of the reactants = 200 KJ

        The Activation Energy in the forward direction =  250 KJ

       

Reaction Path

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


3. Write the following reaction in ΔH notation.         

 

            A   +   B   +   200 kJ          C

 

            A   +  B ----->   C       ΔH=   +200kJ                                                                                                

 

4. Write the following reaction in Standard Notation.

 

            H2    +    I2               2 HI     ΔH =  -250 kJ

 

            H2   +     I2                     2HI   +   250 kJ                                                                                       

 

5. Write in Standard Notation.

 

2NI3   +   3BaCl2       2NCl3    +    3BaI2         ΔH =   175 kJ   

 

            2NI3    +   3BaCl2   +  175 kJ      2NCl3    +   3BaI2                                                                                                                      

 

6. Write in ΔH  notation.

 

2AlBr3   +   3BaF2           2AlF3    +    3BaBr2   +   276 kJ

 

            2AlBr3   +   3BaF2         2AlF3   +   3BaBr2                       ΔH=  -267 kJ                                                                                                 

 

 

Draw the potential energy diagram for the following reactions.

 

7.                                 Potential energy of reactants =                        250 kJ             

                                    Potential Energy of activated complex =         350 kJ

                                    Potential Energy of the products =                  300 kJ

 


 

 

 

 

 

 

 

 

 

 


                                                           

 

 

 

 

a) How does the potential energy change as the reaction proceeds?               Increases       

b) How does the kinetic energy change as the reaction proceeds?                  Decreases      

c) Is the reaction exothermic or endothermic?                                                 Endothermic  

d) What is the value of   ΔH?                                                                          ΔH=  +50kJ   

 

If a catalyst was added, what would happen to the energies of the:

e) Reactants?                                                                                                   Nothing          

f) Products?                                                                                                     Nothing          

g) Activated Complex?                                                                                   Decrease       

h) If a catalyst was added what would happen to the rate?                             Increase         

Draw the potential energy diagram for the following reactions.

 

8.                                 Potential energy of reactants =                        350 kJ             

                                    Activation Energy =                                        100 kJ

                                    Potential Energy of the products =                  250 kJ


 

 

 

 

 

 

 

 

 

 

 


                                                           

 

 

 

 

a) How does the potential energy change as the reaction proceeds?               Decreases                  

b) How does the kinetic energy change as the reaction proceeds?                  Increases                   

c) Is the reaction exothermic or endothermic?                                                 Exothermic                

d) What is the value of ΔH?                                                                            ΔH=  -100kJ              

 

If the concentration of the reactants was increased, what would happen to the energies of the:

 

e) Reactants?                                                                                                   Nothing                      

f) Products?                                                                                                     Nothing                      

g) Activated Complex?                                                                                   Nothing                      

h) What would happen to the rate?                                                                  Increase                     

Draw the potential energy diagram for the following reactions.

 

9.                                 Potential energy of reactants =                        200 kJ             

                                    Potential Energy of activated complex =         400 kJ

                                    ΔH =                                                               150 kJ


 

 

 

 

 

 

 

 

 

 


           

                       

 

 

a)  How does the potential energy change as the reaction proceeds?                          Increases                       

b)  How does the kinetic energy change as the reaction proceeds?                             Decreases                       

c)  Is the reaction exothermic or endothermic?                                                            Endothermic              

d)  What is the value of   ΔH?                                                                                     ΔH=  150 kJ                   

If the temperature was increased, what would happen to the energies of the:

e)  Reactants?                                                                                                              Nothing                       

f)  Products?                                                                                                                Nothing                       

g)  Activated Complex?                                                                                              Nothing                       

h)  What would happen to the rate?                                                                             Increase                       

 

 

 

 

 

 

 

 

10.                               Potential energy of products =                                     50 kJ               

                                    Potential Energy of activated complex =         400 kJ

                                    ΔH=                                                                -50 kJ


 

 

 

 

 

 

 


           

 

 

 

Reaction Path

 
 

 

 

 


a) How does the potential energy change as the reaction proceeds?               Decreases                  

b) How does the kinetic energy change as the reaction proceeds?                  Increases                   

c) Is the reaction exothermic or endothermic?                                                             Exothermic                

d) What is the value of   ΔH?                                                                          ΔH= -50kJ                 

 

If the surface area of the reactants was increased, what would happen to the energies of the:

 

e) Reactants?                                                                                                   Nothing                      

f) Products?                                                                                                     Nothing                      

g) Activated Complex?                                                                                               Nothing                       

h) What would happen to the rate?                                                                  Increase                     

 

 

11. What is the only thing, other than changing the reaction that will change the potential energy diagram? Describe how it will effect the diagram and the rate.

 

            Catalyst          Lowers Ea alloys more low energy collisions to be successful and increase the rate.                                                                                                      

 


12.  Label each  interval on the potential energy diagram.                  a      b          c          d       e

 


                                                                                                                

a)         Ea (forward) (catalyzed)                 

PE

 
 


b)         Ea (reverse)(catalyzed)

 

c)          ΔH

 

d)         Ea (forward) (uncatalyzed)

Reaction Path

 
 


e)         Ea (reverse) (uncatalyzed)

 

12.  Label each interval on the potential energy diagram.

 

 

 

 

                                                                                                a       b        c                     d          e

a)         Ea (forward) (uncatalyzed) 


 


b)         Ea (forward) (catalyzed)                 

 

c)         ΔH     

 

d)         Ea (reverse) (uncatalyzed)              

 

e)         Ea (reverse) (catalyzed)                                                      

 

 

 

 

 

 

Ws # 5   Mechanisms

 

1.                                 OCl-    +     H2O                    HOCl   +   OH-

                                    HOCl    +    I-          HOI    +    Cl-

                                    HOI    +   OH-                 H2O    +    OI-

 

i)         The net chemical equation is:              OCl-   +   I-   +    Cl-   +OI-

ii)        The reaction intermediates are:                       HOCl      HOI     OH-

iii)       The catalyst is:                                                H2O

 

 

2.                                  Br2                          2Br                                                      fast

                                    Br    +   OCl2                         BrOCl    +    Cl                     slow

                                    Br    +   Cl                                   BrCl                                fast

 

i)         The net chemical equation is:              Br2   +   OCl2       BrOCl      +   BrCl

ii)        The reaction intermediates are:                       Cl  & Br

iii)       The catalyst is:                                                None

iv)       The rate determining step is                2

v)         If the concentration of Br2 is increased will the rate of the reaction increase? Explain your answer.   

No because it is not in the rate determining step.                                                                                                                                                                                                                                                                          

vi) If the concentration of OCl2 is increased will the rate of the reaction increase? Explain your answer.               

Yes because, OCl2 is in the rate determining step.                                                                                                                                                                                                                                                            

 

3. The mechanism for the catalytic decomposition of formic acid is shown below.

 

step 1               HCOOH   +   H+       [HCOOHH]+   

 

step 2               [HCOOHH]+            [HCO]+    +    HOH

 

step 3               [HCO]+                 CO    +    H+

 

  The potential energy diagram is:


 

 


                        190

                       

                        180

 

                        170

 

                        160

                       

                        150

 

 

Reaction Path

 
 

 

 

 

 

 

 

 


i) The catalyst is                                                                                  H+                                Crosses out from left to right

ii) The rate determining step is                                                                       Two                             Highest Ea

iii) ΔH  =                                                                                            +10 kJ                         From start to end

iiv) The forward activation energy is                                                  40 kJ                           Reactants to the highest point

iv) The reverse activation energy is                                                    30 kJ                           Products to the highest point

v) The enthalpy of [HCOOHH]+ is                                                      160 kJ                         After one hump         

vi) Is the reaction exothermic or endothermic?                                               Endo                           Uphill

vii) Which chemical formula has the greatest potential energy?                      (HCO)+   +   HOH   Highest point on graph         

viii) Which chemical formula has the greatest kinetic energy?                        HCOOH   +   H+            Lowest point on graph          

ix) Does this reaction absorb or release kinetic energy?                                 Absorb because it is endothermic (uphill)                  

           

 

4. Define and remember the following definitions.

mechanism                   A sequence of steps that determines the overall reaction.                                                                                                            

activation energy         The minimum energy required in a successful collision.                                                                                                                

rate determining step   The slowest step in a reaction mechanism.                                                                                                             

catalyst                                    A substance that increases the rate of a chemical reaction by providing a alternate mechanism with lower activation energy. reaction intermediate A chemical species produced in a reaction mechanism and then consumed in a later step.

endothermic                 A reaction that absorbs energy                                                                                                                   

exothermic                   A reaction that produces energy                                                                                         

activated complex       A unstable reaction intermediate with high potential energy and low kinetic energy.                                                                      

ΔH                               The change in enthalpy or heat content for a reaction.                                                                                         

reaction rate                The change in a reactant or product per unit of time.                                                                                                                   

5. The catalyzed decomposition of acetaldehyde has an overall reaction of:

CH3CHO      CH4     +    CO  . Determine step 2 of the reaction mechanism.

A proposed mechanism is:

step 1               CH3CHO     +    I2       CH3I    +   HI   +  CO

step 2              HI    +    CH3I       I2     +      CH4                                       This is the only step 2 that will give the overall reaction below.     

overall             CH3CHO      CH4     +    CO

6. The following reaction has an overall reaction of:

2Ce4+        +      Tl+              2Ce3+      +         Tl3+

Determine step 2 of the reaction mechanism.

A proposed mechanism is:

step 1               Ce4+        +      Mn+2                         Ce3+     +         Mn3+

step 2              Ce4+        +     Mn3+                        Ce3+   +          Mn4+                This is the only step 2 that will give the overall reaction below

step 3               Mn4+        +      Tl+                           Tl3+     +         Mn2+

                       

overall             2Ce4+        +      Tl+              2Ce3+      +         Tl3+

 

7. A reaction has a overall equation of: Br2   +   OCl2      BrOCl   +   BrCl . Determine step 3 of the mechanism.    

step 1               Br2      2Br

                                    step 2               Br   +   OCl2       BrOCl    +   Cl

                                    step 3              Br   +   Cl       BrCl                         This is the only step 3 that will give the overall reaction below                  

                                   

            overall             Br2   +   OCl2      BrOCl   +   BrCl

 

List two intermediates:                        Br        Cl                   

 

8. Complete the following mechanism.

 

step 1                           NO    +            Pt                 NOPt                                                 needed for next step

step 2                           NOPt   +          NO        O2Pt          +          N2                                O2Pt needed for next step and N2 needed to be a product

step 3                           O2Pt        O2    +    Pt

overall                         2NO         N2     +   O2

 

Identify the catalyst                                         Pt                                            Crosses out from left to right

 

Identify the two intermediates            NOPt              O2Pt                                   Crosses out from right to left

9. Draw a collision energy distribution diagram for a reaction where the y-axis is fraction of collisions and the x axis is collision energy. Draw the Ea line showing about 10% of the collisions having sufficient energy. Draw the Ea line for the catalyzed reaction where 20% have sufficient energy.


 

 

 

 

 

 

 

 


10. Shade in the area of the collision energy distribution diagram showing those collisions that have the required energy to be successful at the low temperature shown below. Draw the curve that represents the distribution at a higher temperature with a different color. Shade in the area representing the successful collisions at the higher temperature with a new color.