SAT Subject Test Chemistry

PART 2

REVIEW OF MAJOR TOPICS

CHAPTER 9

Rates of Chemical Reactions

Practice Exercises

1. List the five factors that affect the rate of a reaction:

1.

2.

3.

4.

5.

2. The addition of a catalyst to a reaction

(A) changes the enthalpy

(B) changes the entropy

(C) changes the nature of the products

(D) changes the activation energy

3. An increase in concentration

(A) is related to the number of collisions directly

(B) is related to the number of collisions inversely

(C) has no effect on the number of collisions

4. At the beginning of a reaction, the reaction rate for the reactants is

(A) largest, then decreasing

(B) largest and remains constant

(C) smallest, then increasing

(D) smallest and remains constant

5. The reaction rate law applied to the reaction aA + bB → AB gives the expression

(A)    r    [A]b[B]a

(B)    r    [AB]a[A]b

(C)    r    [B]a[AB]b

(D)    r    [A]a[B]b

Answers and Explanations

1. (1) Nature of the reactants
(2) Surface area exposed
(3) Concentrations
(4) Temperature
(5) Presence of a catalyst

2. (D) When a catalyst is added to a reaction, it is used to either increase or decrease the activation energy needed for the reaction to occur. When the activation energy is decreased, it allows the reaction to occur at a faster rate; conversely, increasing the activation energy slows down the forward reaction.

3. (A) When the concentration of reactants is increased, the number of collisions between reactants is directly affected because there are more reactant units (ions, atoms, or molecules) available.

4. (A) At the beginning of a reaction, the reaction rate of the reactants is the highest because their concentration is the highest. As the reaction progresses, the concentration of the reactants decreases while the concentration of the products increases.

5. (D) For the reaction aA + bB → AB, the reaction rate law would give the expression of r as proportional to
[A]a[B]b.