Q: For the reaction $$2HI(g) \rightarrow H_2$(g) + I_2$(g)$$, which of the following correctly expresses 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 rapid 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 statements about catalysts is TRUE?

Accepted Answer

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

Question 4

For the reaction $$2HI(g) \rightarrow H_2$(g) + I_2$(g)$$, which of the following correctly expresses the rate in terms of the disappearance of HI?

Accepted Answer

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

Question 5

A reaction has a rate law $$	ext{Rate} = k[A][B]^2. If $$the concentration of B is tripled while A is kept constant, by what factor does the rate increase?

Accepted Answer

9

Question 6

Which of the following best describes the effect of temperature on reaction rate according to the collision model?

Accepted Answer

Increasing temperature increases the kinetic energy of molecules, leading to more frequent and energetic collisions.

Question 7

Given the first-order reaction $$A ightarrow B$$, the integrated rate law is $$\ln [A]_t = -kt + \ln [A]_0. If$$ $$k = 5 	imes 10$$^{-5}$$ \ s$$^{-1}$$ and $$[A]_0 = 0.200 \ M$$, what is $$[A]$$ after 10$$,000$$ seconds?

Accepted Answer

$$[A] = 0.121 \ M$$

Question 8

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 for the reaction.

Question 9

The half-life for a first-order reaction is given by $$t_{1/2} = \frac{0.693}{k}. If$$ $$k = 2.0 	imes 10$$^{-3}$$ \ s$$^{-1}$$, what is the half-life?

Accepted Answer

$$t_{1/2} = 346.5 \ s$$

Question 10

Which of the following is an example of heterogeneous catalysis?

Accepted Answer

Hydrogenation of ethylene using a platinum catalyst.

Question 11

For the reaction $$NH_4^+ (aq$$) + $$NO_2^- (aq$$) ightarrow $$N_2 (g) + 2H_2O (l$$)$$, the rate law is $$	ext{Rate} = k[$$NH_4$$^+][$$NO_2$$^-]$$. What is the overall order of the reaction?

Accepted Answer

Second order

Question 12

Which of the following best describes an intermediate in a reaction mechanism?

Accepted Answer

A species that is formed in one step and consumed in a subsequent step.

Question 13

The Arrhenius equation is $$k = A e$$^{-E_a/RT}$$. If the activation energy E_a$ increases, what happens to the rate constant k$ (assuming all other factors remain constant)?

Accepted Answer

The rate constant $$k$$ decreases.

Question 14

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

Accepted Answer

The color of the reactants

Question 15

A reaction is found to be zero order in reactant A. What will happen to the rate if the concentration of A is doubled?

Accepted Answer

The rate will remain unchanged.

Question 16

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 proceed.

Question 17

If the rate law for a reaction is $$	ext{Rate} = k[A]^2$$, what are the units of the rate constant $$k$$?

Accepted Answer

$$M^{-1}$$ $$s^{-1}$$

Question 18

Which of the following is true about the initial rate of a reaction?

Accepted Answer

It is the instantaneous rate at $$t = 0$$ and is typically the fastest rate observed.

Question 19

Which of the following is a correct statement about the effect of a catalyst on a reaction coordinate diagram?

Accepted Answer

A catalyst lowers the activation energy barrier, making it easier for reactants to form products.

Chemical Kinetics: Reaction Rates and Mechanisms

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