Chem 162-2011 Chapter 13B-Some Kinetics practice problems -...

PRACTICE PROBLEMS
CHEM 162-2009 EXAM I
CHAPTER 13B - KINETICS
• REACTION MECHANISMS, ACTIVATION ENERGY & CATALYSTS CONCEPTS
• REACTION MECH., ACTIVATION ENERGY & CATALYSTS CALCULATIONS
E. Tavss, PhD
REACTION MECHANISMS, ACTIVATION
ENERGY & CATALYSTS CONCEPTS
1

46 Chem 162-2007 Final exam + answers
Chapter 13 - Kinetics
Reaction mechanisms, activation energy and catalysts concepts
Which statement regarding the collision theory of kinetics is true ?
A. All reactants that collide with enough energy form products.
B
. Only a fraction of the collisions with enough energy to form products actually
proceeds from reactants to products.
C. All reactants that collide with the correct orientation form products.
D. Reactants that collide with kinetic energy greater than ∆H go on to form
products.
E. E
a
of the reverse reaction is always greater than E
a
of the forward reaction.
A. False. The steric factor is important also. Even if there is enough energy in the
collision, if the molecules aren’t oriented properly then products won’t form. In
addition, there is an equilibrium, which is to say that the transition state dissociates
partly back to reactants and partly to products, depending on ∆ G.
B. True. Even if they have enough energy their orientation may be wrong. In
addition, there is an equilibrium, which is to say that the transition state dissociates
partly back to reactants and partly to products, depending on ∆ G.
C. False. The energy of activation factor is important also. Even if the molecules
collide in the correct orientation, if they don’t have enough energy they won’t form
products. In addition, there is an equilibrium, which is to say that the transition state
dissociates partly back to reactants and partly to products, depending on ∆ G.
D. False. ∆ H is irrelevant to the energy necessary to have fruitful collisions. The
energy has to be at least that of the energy of activation. In addition, there is an
equilibrium, which is to say that the transition state dissociates partly back to reactants
and partly to products, depending on ∆ G.
E. False. E
a
of the reverse reaction is greater than E
a
of the forward reaction only
when the enthalpy of the product is less than the enthalpy of the reactant.
2

14. CHEM 162-2007 EXAM I + ANSWERS
CHAPTER 13 – KINETICS
REACTION MECHANISMS, ACTIVATION ENERGY & CATALYSTS CONCEPTS
Which statement is not correct regarding the function of a catalyst?
A) It lowers the activation energy.
B) It changes the mechanism of a reaction.
C) It affects the rate of a chemical reaction.
D) It lowers the energy of the product causing the reaction to be more exothermic.
E) It is regenerated in the reaction.
(A) True.
(B) True.
(C) True.
(D)
False. A catalyst only lowers the energy of activation. It has no effect on the energy of
the reactants or the products.