Kinetics           Quiz 4  Potential Energy Diagrams

1.          A catalyst increases the rate of a reaction by

A.        Increasing the concentration of the reactant(s)

B.        Decreasing the concentration of the reactant(s)

C.        Increasing the activation energy of the overall reaction

D.        Decreasing the activation energy of the overall reaction

2.         Consider the following Reaction: ½ N2(g)  +  ½  O2(g)  → NO(g)

∆H = +90 kJ/mol  NO

The correct equation including the heat term is

A.        N2(g) + O2(g) +90 kJ ------- > 2NO(g)

B.        N2(g) + O2(g) +180 kJ ------- > 2NO(g)

C.        N2(g) + O2(g)  ------- > 2NO(g)   +90kJ

D.        N2(g) + O2(g)  ------- > 2NO(g)   +180kJ

3.         A forward reaction has an activation energy of 50 kJ and a ∆H of –100 kJ. The PE diagram, which describes this reaction, is

4.       Consider the following potential  energy diagram The Activation energy for the forward reaction is

A.        25 kJ

B.        50 kJ

C.        75 kJ

D.        125 kJ

5.         Consider the following reaction: ½ H2(g)  +  ½ I2(g)   ------- >  HI(g)

The activation energy for the formation of HI is 167 kJ and for the decomposition of HI is 139 kJ. The reaction for the formation of HI is

A.        Exothermic and the ∆H = -28 kJ

B.        Exothermic and the ∆H = +28 kJ

C.        Endothermic and the ∆H = -28 kJ

D.        Endothermic and the ∆H = +28 kJ

6.         Consider the following potential energy diagram The energy interval the represents the activation energy for the reverse reaction is

A.        I

B.        II

C.        III

D.        IV

7.         As reactant molecules approach each other

A.        Heat is released

B.        A reaction intermediate forms

C.        Kinetic energy changes to potential energy

D.        Potential energy changes to kinetic

8.         Which of the following equations represents an endothermic reaction?

A.        N204(g)  +  59 kJ ------- > 2NO2(g)

B.        2H2(g)  +  02(g)  ------- > 2H2O(l)  +  572 kJ

C.        2BrCl(g) – 29.3 kJ ------ > Br2(g) +  Cl2(g)

D.        C(s) + O2(g) ------- > CO2(g)     ∆H = -394 kJ

9.         Consider the following potential energy diagram The interval representing ∆H for the reverse reaction is

A.        1

B.        2

C.        3

D.        4

10.       Which of the following corresponds to the fastest reaction at room temperature 11.       When a catalyst is added to a reaction, ∆H will

A.        Increase slowly

B.        Remain constant

C.        Decrease slowly

D.        Increase rapidly due to alternate pathway

12.       Consider the following potential energy diagram that represents two different reactions. Which of the following statements is correct? A                                                                     B

A.        Reactions A and B are both exothermic

B.        Reactions A and B are both endothermic

C.        Reaction A is exothermic and reaction B is endothermic

D.        Reaction A in endothermic and reaction B is exothermic

13.       Consider the following reaction: ½ H2(g)  +  ½ I2(g)  ------- > HI(g)      ∆H = +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 14.       Consider the following potential energy diagram for 14 to 16

Which of the following are the values for the activation energy Ea and change in enthalpy ΔH for the forward reaction?

Ea(kJ)                          ΔH(kJ)

A.        300                              –50

B.        150                              +50

C.        100                              –50

D.        100                              +50

15.       Which of the following are the values for the activation energy Ea and change in enthalpy ΔH for the reverse reaction?

Ea (kJ)                         ΔH (kJ)

A.        300                              –50

B.        150                              +50

C.        100                              –50

D.        100                              +50

16.       What is the PE of the reactants and activated complex?

Reactants (kJ)              Activated Complex (kJ)

A.        50                                50

B.        300                              150

C.        200                              200

D.        150                              300

17.       Which of the following would have a positive value for ΔH?

I.          the evaporation of alcohol

II.         the burning of a candle

III.       an explosive reaction

IV.       a chemical cold pack

A.        III only

B.        IV only

C.        I and IV

D.        II and III

18.       Which of the following represents the value for the activation energy of the forward reaction in an equilibrium system?

A.        Ea forward      =          Ea reverse   +   ΔH

B.        Ea forward      =          Ea reverse   -   ΔH

C.        Ea forward      =          ΔH -    Ea reverse

D.        Ea forward      =          ΔH -    Ea forward

19.       Consider the following reaction:         H2(g)    +    Cl2(g)       2HCl(g)

As a molecule of H2 approaches a molecule of Cl2 on a collision course, how do the KE and PE change?

KE                               PE

A.                    increases                     decreases

B.                    decreases                    increases

C.                    decreases                    decreases

D.                    increases                     increases

20.       Consider the following reaction:         H2(g)    +    Cl2(g)       2HCl(g)

As the activated complex forms changes to HCl

KE                               PE

A.                    increases                     decreases

B.                    decreases                    increases

C.                    decreases                    decreases

D.                    increases                     increases

21.       The activated complex is best described as:

A.        stable               maximum PE               minimum KE

B.        stable               minimum PE                maximum KE

C.        unstable           maximum PE               minimum KE

D.        unstable           minimum PE                maximum KE

22.       In a certain reaction ΔH = -136 kJ and Ea reverse = 236 kJ.  Which of the following is true of its forward reaction?

A.        The reaction is exothermic and Ea = -100 kJ.

B.        The reaction is exothermic and Ea = 100 kJ.

C.        The reaction is endothermic and Ea = 372 kJ.

D.        The reaction is endothermic and Ea = 232 kJ

23.       In a certain reaction ΔH = -136 kJ and Ea = 96 kJ.  Which of the following is true about the reverse reaction?

A.        The reverse reaction is exothermic and Ea = -40 kJ.

B.        The reverse reaction is exothermic and Ea = 40 kJ.

C.        The reverse reaction is endothermic and Ea = 96 kJ.

D.        The reverse reaction is endothermic and Ea = 232kJ

24.       Consider the following information for a reversible chemical reaction:

Forward activation energy 20 kJ                     Reverse activation energy 30 kJ

Which of the following describes the reaction type and enthalpy change for the forward reaction?

Reaction Type             ΔH Value

A.        exothermic                   10 kJ

B.        exothermic                  -10 kJ

C.        endothermic                 10 kJ

D.        endothermic                -10 kJ

25.       Consider the following information for a reversible chemical reaction:

Forward activation energy 20 kJ                     Reverse activation energy 30 kJ

Which of the following describes the reaction type and enthalpy change for the reverse reaction?

Reaction Type             ΔH Value

A.        exothermic                   10 kJ

B.        exothermic                  -10 kJ

C.        endothermic                 10 kJ

D.        endothermic                -10 kJ

26. Which of the following is true for the forward reaction?

Reaction          PE of Activated Complex (kJ) ΔH (kJ)

A.        catalyzed                     100                                          -50

B.        uncatalyzed                  300                                          -50

C.        catalyzed                     250                                          +50

D.        uncatalyzed                  150                                          -50

27.       An activated complex can be described as

A.        a particle of maximum KE and minimum PE.

B.        a stable particle found in a reaction mechanism.

C.        an unstable particle that is neither reactant nor product.

D.        a particle which is first used then regenerated in a reaction mechanism.

28.       Which of the following describes the Ea of a fast reaction and the stability of           its activated complex?

Ea                    Activated Complex

A.        small               unstable

B.        small               stable

C.        large                unstable

D.        large                stable

29.       As an activated complex changes into products, what changes occur in the chemical bonds of the activated complex and the PE of the system?

Bonds                          PE

A.        form                             increases

B.        form                             decreases

C.        break                           increases

D.        break                           decreases

30.       As reactants change into an activated complex, what changes occur in the chemical bonds of the activated complex and the PE of the system?

Bonds                          PE

A.        form                             increases

B.        form                             decreases

C.        break                           increases

D.        break                           decreases Use this diagram for 30 -32

31.       Which of the following describes the reverse reaction?

Activation Energy (kJ)                        ∆H (kJ)

A.        uncatalyzed                              200                                          −100

B.        catalyzed                                 200                                          −100

C.        uncatalyzed                              300                                          +100

D.        catalyzed                                 300                                          +100

32.       Consider the following reaction:

CH4     +     Cl2     →   CH2Cl2     +     H2

Which answer best describes the activated complex?

Formula                                   KE relative to reactants

A.        CH4                             higher

B.        CH4                             lower

C.        CH4Cl2                        higher

D.        CH4Cl2                        lower