Q: For the reaction $$2NO_2(g) \rightarrow 2NO(g) + O_2$(g)$$, which expression correctly represents the rate of the reaction in terms of the change in concentration of $$NO_2$$?

$$\text{Rate} = -\frac{1}{2} \frac{\Delta[NO_2$]}{\Delta t}$$

Question 1

Which of the following statements best describes the effect of a catalyst on a chemical reaction?

Accepted Answer

A catalyst provides an alternative reaction pathway with a lower activation energy.

Question 2

For the reaction $$2NO_2(g) \rightarrow 2NO(g) + O_2$(g)$$, which expression correctly represents the rate of the reaction in terms of the change in concentration of $$NO_2$$?

Accepted Answer

$$	ext{Rate} = -\frac{1}{2} \frac{\Delta[NO_2$]}{\Delta t}$$

Question 3

A reaction is found to be first order with respect to $$A$$ and second order with respect to $$B. $$Which is the correct rate law for this reaction?

Accepted Answer

$$	ext{Rate} = k[A][B]^2$$

Question 4

If the concentration of reactant $$A in a $$zero-order reaction is initially $$0.50\,M$$, what will its concentration be after one half-life?

Accepted Answer

$$0.25\,M ($$since zero-order half-life is $$t_{1/2} = \frac{[A]_0}{2k})$$

Question 5

Which plot would yield a straight line for a first-order reaction?

Accepted Answer

$$\ln[A] vs. $$time

Question 6

The Arrhenius equation relates the rate constant $$k to $$which of the following variables?

Accepted Answer

Activation energy and temperature

Question 7

For the reaction $$A ightarrow B$$, the rate law is $$	ext{Rate} = k[A]. If$$ $$[A] is $$doubled, what happens to the rate?

Accepted Answer

The rate doubles.

Question 8

Which of the following is true about the rate-determining step in a reaction mechanism?

Accepted Answer

It is the slowest step and controls the overall reaction rate.

Question 9

A reaction has the following rate law: $$	ext{Rate} = k[NO_2$]^2. $$What is the overall order of the reaction?

Accepted Answer

Second order

Question 10

Which factor does NOT directly affect the rate constant $$k in $$the rate law $$	ext{Rate} = k[A][B]$$?

Accepted Answer

Concentration of reactants

Question 11

In collision theory, which two conditions must be met for a reaction to occur when molecules collide?

Accepted Answer

Molecules must have sufficient kinetic energy and collide in the correct orientation.

Question 12

For a first-order reaction, the half-life is given by which equation?

Accepted Answer

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

Question 13

Which of the following best explains why increasing temperature generally increases reaction rate?

Accepted Answer

It increases the fraction of molecules with enough energy to overcome the activation barrier.

Question 14

A reaction mechanism consists of the following steps:
Step 1: $$A + B \rightarrow C ($$slow)
Step 2: $$C + D \rightarrow E ($$fast)
What is the rate law for the overall reaction?

Accepted Answer

$$	ext{Rate} = k[A][B]$$

Question 15

Which statement about reaction intermediates is correct?

Accepted Answer

Intermediates are formed and consumed during the reaction mechanism.

Question 16

Which of the following is an example of heterogeneous catalysis?

Accepted Answer

A platinum surface catalyzing the reaction of $$C_2H_4(g)$$ and $$H_2(g$$)$$ to form C_2H_6(g$$)$$.

Question 17

The rate law for an elementary bimolecular step $$A + B \rightarrow$$ products is:

Accepted Answer

$$	ext{Rate} = k[A][B]$$

Question 18

Which of the following is NOT a requirement for a proposed reaction mechanism to be valid?

Accepted Answer

The mechanism must consist of only unimolecular steps.

Question 19

In the context of enzyme catalysis, what is the role of the active site?

Accepted Answer

It binds the substrate and orients it for reaction.

Question 20

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

Accepted Answer

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

Chemical Kinetics: Rates of Chemical Reactions

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