Question 1

A person is sprinkling calcium chloride on an icy sidewalk, as shown in the image. Which of the following actions would most effectively increase the rate at which the ice melts, according to collision theory?

Accepted Answer

Breaking the ice into smaller pieces before sprinkling the calcium chloride

Question 2

According to collision theory, which of the following is NOT required for a chemical reaction to occur between two reactant molecules?

Accepted Answer

The reactant molecules must collide with a catalyst present

Question 3

Which of the following best describes the role of activation energy ($$E_a) in a $$chemical reaction?

Accepted Answer

It is the minimum energy required for reactants to form an activated complex

Question 4

A Maxwell–Boltzmann distribution graph shows the number of molecules versus their kinetic energy. What happens to the area under the curve representing molecules with energy greater than $$E_a$$ when temperature increases?

Accepted Answer

It increases

Question 5

Which of the following statements about catalysts is TRUE?

Accepted Answer

A catalyst provides an alternative pathway with lower activation energy

Question 6

Consider the reaction: $$2\ \mathrm{BrNO}(g) \rightarrow 2\ \mathrm{NO}(g) + \mathrm{Br}_2(g). $$According to collision theory, why might some collisions between BrNO molecules not result in a reaction?

Accepted Answer

Both A and B

Question 7

Which of the following changes would NOT increase the rate of a reaction between a solid and a liquid reactant?

Accepted Answer

Decreasing the temperature of the system

Question 8

In an exothermic reaction, which of the following is true about the enthalpy change ($$\Delta H$$)?

Accepted Answer

$$\Delta H is $$negative

Question 9

Why do reactions between ions in aqueous solution generally occur faster than reactions between covalently bonded molecules?

Accepted Answer

Ions do not require bond breaking to react

Question 10

Which of the following best explains why powdered zinc reacts faster with hydrochloric acid than zinc chunks?

Accepted Answer

Powdered zinc has a greater surface area for collisions

Question 11

A reaction has an activation energy of $$75\ \mathrm{kJ/mol}. If a $$catalyst lowers the activation energy to $$40\ \mathrm{kJ/mol}$$, what is the effect on the reaction rate at a constant temperature?

Accepted Answer

The reaction rate increases

Question 12

Which of the following is the best analogy for the role of activation energy in a chemical reaction?

Accepted Answer

A hill that must be climbed before rolling down

Question 13

Which of the following would NOT increase the number of effective collisions in a reaction mixture?

Accepted Answer

Decreasing the surface area of a solid reactant

Question 14

Which of the following statements about the activated complex is correct?

Accepted Answer

It represents the maximum potential energy point during a reaction

Question 15

If the temperature of a reaction mixture is increased from $$T_1 to$$ $$T_2$$, what happens to the fraction of molecules with kinetic energy greater than the activation energy?

Accepted Answer

It increases

Question 16

Which of the following best describes why increasing the concentration of a reactant increases the reaction rate?

Accepted Answer

It increases the number of collisions per unit time

Lesson 6.3: Explaining Reaction Rates: Collision Theory and Factors Affecting Reaction Rate

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