Q: For the reaction $$2HI(g) \rightarrow H_2$(g) + I_2$(g)$$, which of the following is the correct expression for the rate in terms of the disappearance of HI?

$$\text{Rate} = -\frac{1}{2} \frac{\Delta [HI]}{\Delta t}$$

Question 1

Which of the following best explains why a powdered medicine dissolves and acts faster in the stomach than the same medicine in tablet form?

Accepted Answer

Powdered medicine has a larger surface area, allowing for more immediate interaction with stomach fluids.

Question 2

A reaction is carried out at two different concentrations of reactant A. When the concentration of A is doubled, the rate of the reaction quadruples. What is the order of the reaction with respect to A?

Accepted Answer

Second order

Question 3

Which of the following is the correct integrated rate law for a first-order reaction?

Accepted Answer

$$\ln \left( \frac{[A]_t}{[A]_0} \right) = -kt$$

Question 4

Which of the following statements about catalysts is TRUE?

Accepted Answer

A catalyst increases the rate of a reaction by lowering the activation energy.

Question 5

For the reaction $$2HI(g) \rightarrow H_2$(g) + I_2$(g)$$, which of the following is the correct expression for the rate in terms of the disappearance of HI?

Accepted Answer

$$	ext{Rate} = -\frac{1}{2} \frac{\Delta [HI]}{\Delta t}$$

Question 6

A reaction has a half-life that does not depend on the initial concentration of the reactant. What is the order of this reaction?

Accepted Answer

First order

Question 7

Which of the following best describes the effect of increasing temperature on the rate constant $$k$$ according to the Arrhenius equation?

Accepted Answer

Increasing temperature increases $$k$$ because more molecules have energy greater than $$E_a.$$

Question 8

Given the Arrhenius equation $$k = A e$$^{-E_a/RT}$$, what does the parameter A$ represent?

Accepted Answer

The frequency factor, related to the frequency and orientation of collisions.

Question 9

Which of the following is a correct statement about the rate-determining step in a multistep reaction mechanism?

Accepted Answer

It is the slowest step and determines the overall rate law.

Question 10

A reaction is found to be first order in $$A$$ and second order in $$B. $$What is the overall order of the reaction?

Accepted Answer

Third order

Question 11

Which of the following best explains why food spoils more slowly in a refrigerator than at room temperature?

Accepted Answer

Lower temperature decreases the rate constant, so fewer molecules have enough energy to react.

Question 12

For a second-order reaction with respect to $$A$$, which of the following is the correct integrated rate law?

Accepted Answer

$$\frac{1}{[A]_t} = kt + \frac{1}{[A]_0}$$

Question 13

Which of the following is NOT a factor that affects the rate of a chemical reaction?

Accepted Answer

The color of the reactants

Question 14

Which of the following is a correct expression for the half-life of a first-order reaction?

Accepted Answer

$$t_{1/2} = \frac{0.693}{k}$$

Question 15

Which of the following best describes a reaction intermediate?

Accepted Answer

A species formed in one step and consumed in a subsequent step of a reaction mechanism.

Question 16

Which of the following is true about the rate law for an elementary reaction?

Accepted Answer

The rate law can be written directly from the molecularity of the elementary step.

Question 17

Which of the following is a real-life example of heterogeneous catalysis?

Accepted Answer

The use of platinum in catalytic converters to convert CO to CO$$_2 in $$car exhaust.

Question 18

Which of the following best describes the lock-and-key model of enzyme catalysis?

Accepted Answer

The substrate fits into the enzyme's active site, allowing the reaction to occur.

Question 19

If the activation energy ($$E_a) $$for a reaction is 100 kJ/mol and the temperature is 300 K, what is the fraction of molecules with energy greater than or equal to $$E_a$$? (Use $$R = 8.314 J/$$mol·K)

Accepted Answer

$$f = e$$^{-E_a/RT}$$ = e$$^{-100,000/(8.314 	imes 300)}$$

Chemical Kinetics: Factors Affecting Reaction Rates and Mechanisms

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