Chemistry 12                  Kinetics Practice Test # 2              Iannone 

 

1.         Which of the following units could be used to express the reaction rate?

 

            A.        mL/s

            B.        mL/g

            C.        g/mL

            D.        mL/mol

 

2.         Consider the reaction:             Zn(s)  +  2HCl(aq)  →  ZnCl2(aq)  +  H2(g)

The rate of production of ZnCl2, can be increased by

 

            A.        decreasing the [HCl].

            B.        increasing the temperature

            C.        increasing the volume of H2.

            D.        decreasing the surface area of Zn.

 

3.         The statement, the minimum energy needed for a successful collision, defines

 

            A.        enthalpy.

            B.        activation energy.

            C.        the ΔH of the reaction.

            D.        the activated complex.

 

4.         As an activated complex changes to products,

 

            A.        potential energy changes to kinetic energy.

            B.        kinetic energy changes to potential energy.

            C         kinetic energy changes to activation energy.

            D.        potential energy changes to activation energy.

 

5.         Which of the following is most likely to have the greatest rate at room temperature.

 

            A.        2H2(g)  +  O2(g)  →  2H2O(l)

            B.        2Ag+(aq)  +  CrO42-(aq)  →  Ag2CrO4(s)

            C.        Pb(s)  +  2HCl(aq)   → PbCl2(aq)  +  H2(g)

            D.        CH4(g)  +  2O2(g)  →  CO2(g)   +  H2O(g)

 

 

 

 

 

 

 

 

6          Consider the following PE diagram for an uncatalyzed and catalyzed reaction

 

           

 

 

 

 

 

 


           

 

 

 

 

 

 

Which of the following describes the forward catalyzed reaction?

 

                        Activation Energy (kJ)            ΔH (kJ)          

 

            A.                    10                                -15

            B.                    10                                15

            C.                    25                                -15

            D.                    25                                15

 

 

 

7.         A substance that increases the rate of a reaction without appearing in the equation for the overall reaction is a(an)

 

            A.        product

            B.        catalyst

            C.        reactant

            D.        intermediate

 

8.         Activation energy can be described as the

 

            A.        energy of motion

            B.        energy of the activated complex.

            C.        energy difference between the reactants and the products.

            D.        energy difference between the reactants and the activated complex.

 

9.         What effect does a catalyst have on a reaction?

 

            A.        It changes the ΔH of a reaction.

            B.        It increases the kinetic energy of the reactants.

            C.        It decreases the potential energy of the products.

            D.        It provides a reaction mechanism with a lower activation energy.

 

10.       Consider the following reaction involving 1.0 g of powdered zinc:

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

 

            Trial                Temperature (0C)        Concentration of HCl 

 

            1                      40                                3.0

            2                      20                                3.0

            3                      40                                6.0

 

            The rates in order of fastest to slowest are

 

            A.        1, 2, 3

            B.        2, 1, 3

            C.        3, 1, 2

            D.        3, 2, 1

 

11.       Consider the following potential energy diagram for a reversible reaction:

 

           

 

 

 

 

 

 

 

 

 

 

 


Which of the following describes the system above?

 

                        Reaction          Activation Energy (kJ)            ΔH (kJ)

 

            A.                    reverse           10                                            -20

            B.                    reverse                        10                                            -30

            C.                    forward           30                                            +10

D.                    forward           20                                            +30

 

12.       An activated complex is a chemical species that is

 

            A.        stable and has low PE.

            B.        stable and has high PE.

            C.        unstable and has low PE.

D.        unstable and has high PE.

 

13.       Consider the reaction: Ca(s)  + 2H2O(l)  →  Ca(OH)2(aq)  +  H2(g)

 

At a certain temperature, 2.05 g Ca reacts completely in 30.0 seconds. The rate of consumption of Ca is

 

            A.        0.00208 mol/min        

            B.        0.0833 mol/min

            C.        0.102 mol/min

            D.        5.00 mol/min

 

14.       Increasing the temperature of a reaction increases the reaction rate by

 

            I.          increasing frequency of collision

            II.         increasing the kinetic energy of collision

            III.       decreasing the potential energy of the collision

 

            A.        I only.

            B.        I and II only.

            C.        II and III only.

            D.        I, II, and III.

 

15.       A certain reaction is able to proceed by various mechanisms. Each mechanism has a different Ea and results in a different overall rate. Which of the following best describes the relationship between the Ea values and the rates?

 

                                                                                                                                                                                                                                                           

 

 

 

 

 

 

 

 

 

 

 

 

16.       For collisions to be successful, reactants must have

 

            A.        favourable geometry.

            B         sufficient heat of reaction only.

            C.        sufficient potential energy only.

            D.        sufficient kinetic energy and favourable geometry.

 

17.       Consider the following reaction: 1/2 H2(g)  +  1/2 I2(g)  →  HI(g)           ΔH  =  +28 kJ

 

The activation energy for the formation of HI is 167 kJ. The activation energy for the decomposition of HI is

 

            A.        28 kJ

            B.        139 kJ

            C.        167 kJ

            D.        195 kJ

 

18.       Which of the following factors affects the rate of heterogeneous reactions only?

 

            A.        nature of the reactant

            B.        temperature

            C.        surface area of reactants

            D.        concentration of reactants

 

19.       A 25.0 mL sample of hydrogen peroxide decomposes producing 50.0 mL of oxygen gas in 137 s. The rate of formation of O2 in mL/min is

 

            A.        0.182 mL/min

            B.        0.365 mL/min

            C.        10.9 mL/min

            D.        21.9 mL/min

           

20.       Consider the following reaction mechanism:             

 

step 1               2NO  +  H2  →  N2  +  H2O2

step 2               H2O2  +  H2  →  2H2O

 

In this reaction H2 is a

 

            A.        product

            B.        catalyst

            C.        reactant

            D.        reaction intermediate

 

21.       Which of the following properties could be used to measure the rate of the following reaction taking place in an open container?

           

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

           

A.        mass of Zn

B.        solubility of HCl

C.        concentration of Cl-

D.        colour of the solution

 

22.       Consider the following reaction:  N2  +  3H2  →  2NH3

 

            The rate of formation of NH3 is 3.0 mole/min. The rate of consumption of H2 is:

 

            A.        1.5 mole/min

            B.        2.0 mole/min

            C.        4.5 mole/min

            D.        9.0 mole/min

 

23.       Consider the following reaction mechanism:             

           

            Step 1              NO2  +  NO2  →  N2O4

            Step 2              N2O4  +  CO  →  CO2  +  NO  +  NO2

           

In the overall reaction, N2O4 is a

 

            A.        product

            B.        catalyst

            C.        reactant

            D.        reaction intermediate

 

24.       Consider the following mechanism:

 

            Step 1              NO  +  O3  →  NO2  +  O2

            Step 2              O  +  NO2  →  NO  +  O2

 

            The catalyst is

 

            A.        O2

            B.        O3

            C.        NO

            D.        NO2

 

25.       Consider the following reaction: Mg(s)  +  2HCl(aq)  →  MgCl2(aq)  +  H2(g)

 

The rate of this reaction increases when more Mg is added. This change is caused by the

 

            A.        addition of a catalyst

            B.        increase in surface area

            C.        change in the nature of the reactants

            D.        increase in concentration of reactants

 

26.       Consider the following PE diagram

 

 

 

 

 

 

 

 

 

 

 

 

 

 


            The forward reaction can be described as

 

                                    DH                   Ea                    Type

 

A.                    +20                  80                    endothermic

B.                    +20                  60                    exothermic

C.                    -20                   80                    exothermic

D.                    -20                   100                  endothermic

 

27.       Consider the following reaction:  HgO(s)  →  Hg(l)  +  1/2O2(g)

 

            The rate of this reaction can be expressed as

 

            A.        rate  =  [O2}1/2

            B.        rate  =  Δ[O2]/Δt

            C.        rate  =  Δ[Hg]/Δt

            D.        rate  =  Δ[HgO]/Δt

 

28.       Which of the following would react most rapidly?

 

            A.        Powdered Zn in 1.0 M HCl at 25 0C

B.        Powdered Zn in 20 M HCl at 40 0C

C.        A lump of Zn in 2.0 M HCl at 25 0C

D.        A lump of Zn in 1.0 M HCl at 40 0C

 

29.       Addition of a catalyst to a reaction increases the rate because it

 

            A.        increases the value of ΔH

            B.        decreases the value of ΔH

            C.        provides an alternate mechanism with a lower Ea

            D.        provides an alternate mechanism with a higher Ea

 

30.       When a collision occurs between two reactant species which possess between them the minimum kinetic energy a product does not always form. This may be a result of

 

            A.        low temperature

            B.        small surface area

            C.        low concentrations

            D.        unfavourable geometry

 

 

Subjective Answers

 

 

1.         An experiment is done to determine the rate of the following reaction:

           

2Al(s)  +  6HCl(aq)  →  3H2(g)  +  2AlCl3(aq)

 

The following data are collected

Time (s)                      Mass of Flask + Contents (g)

 

0.0                   270.230

30.0                 270.200

60.0                 270.170

 

60.0 s              0.060 g H2      

 

 

Calculate the rate of consumption of Al in mol/min.               (3 marks)

 

 

0.060 g H2           x          60 s         x      1mole H2        x           2 mol Al

 


60.0 s                          1 min               2.0 g                            3 mol H2

 

            =  0.020 mol Al/min

 

2.         Define the term activation energy.

 

            The minimum energy required for a successful collision.

 

 

 

3.         Define the word Activated complex.

 

Unstable reaction intermediate with high potential energy and low kinetic energy.

 

4.         Define the word mechanism.

 

            A sequence of steps that determines the overall reaction.

 

5.         Consider the following reaction mechanism

 

            Step 1                                      ?

           

Step 2              H2  +  Cl  →  HCl  +  H

           

Step 3              H  +  Cl2  →  HCl  +  Cl

 

Step 4              Cl  +  Cl  →  Cl2

 

Overall                        H2  +  Cl2  →  2HCl

 

a)         Write the equation for step 1

 

            Cl2       →        2Cl

 

b)         Identify the reaction intermediate(s)

 

            Cl        H

 

 

6.         Consider the overall reaction:  4HBr  +  O2  →  2H2O  +  2Br2

 

A proposed three-step mechanism is:

 

            Step 1              HBr  +  O2    →   HOOBr

 

            Step 2                                      ?

           

            Step 3              HBr  +  HOBr  →  H2O  +  Br2

 

            Write the equation for step 2.

 

            2HBr  +  HOOBr  →  HOBr  +  H2O  +  Br2

 

 

7.         A student wishes to monitor the rate of the following reaction:         

 

            CaCO3(s)  +  2HCl(aq)  →  CaCl2(aq)  +  CO2(g)  +  H2O(l)

 

Identify two properties that could be used to monitor the rate of the reaction. Describe and explain the changes that would occur.

 

Property 1                               Mass of  CaCO3(s)  over time

 

Change and explanation           Decreases, as reactants are converted into products.

 

Property 2                               Concentration of HCl over time

 

Change and explanation           Decreases, as reactants are converted into products.

 

 

Any two in this list!                Concentration of CaCl2(aq)  over time

                                               

Increases, as reactants are converted into products over time

 

                                                Volume of CO2 over time

                       

Increases, as reactants are converted into products over time

 

                                                Mass of an open beaker over time

 

                                                Decreases as CO2 escapes over time

 

                                                Pressure of a closed system over time

 

                                                Increases as CO2 is produced over time

                                               

 

 

 

 

 

 

 

8.         Carbon burns in air according to the following equation:

 

            C(s)  +  O2(g)  →  CO2(g)

 

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

 

            Increase temperature                        Increase O2 concentration

            Increase the pressure                        Add a catalyst                       

 

Increase C surface area

 

 

 

9.         Sketch the potential energy diagram for an endothermic reaction in the space below. On your diagram clearly label:

 


            i)         the energy of the activated complex

            ii)        the activation energy

            iii)       ΔH