Q: Given the reaction $$\text{H}_2(g) + \text{I}_2(g) \rightarrow 2 \text{HI}(g)$$, what is the correct relationship between the rates of disappearance of $$\text{H}_2$$ and $$\text{I}_2$$ and the rate of appearance of $$\text{HI}$$?

$$\text{Rate} = -\frac{\Delta[\text{H}_2]}{\Delta t} = -\frac{\Delta[\text{I}_2]}{\Delta t} = \frac{1}{2}\frac{\Delta[\text{HI}]}{\Delta t}$$

Question 1

Which of the following best describes the rate of a chemical reaction as shown in the equation $$	ext{Rate} = -\frac{\Delta[	ext{H}_2]}{\Delta t}$$?

Accepted Answer

The rate is the decrease in reactant concentration per unit time, with a negative sign to indicate consumption.

Question 2

Given the reaction $$	ext{H}_2(g) + 	ext{I}_2(g) ightarrow 2 	ext{HI}(g)$$, what is the correct relationship between the rates of disappearance of $$	ext{H}_2$$ and $$	ext{I}_2$$ and the rate of appearance of $$	ext{HI}$$?

Accepted Answer

$$	ext{Rate} = -\frac{\Delta[	ext{H}_2]}{\Delta t} = -\frac{\Delta[	ext{I}_2]}{\Delta t} = \frac{1}{2}\frac{\Delta[	ext{HI}]}{\Delta t}$$

Question 3

A reaction is monitored and the following data are collected: $$[	ext{H}_2]$$ drops from 1.000 M to 0.819 M in 10.0 s. What is the average rate of disappearance of $$	ext{H}_2$$ over this interval?

Accepted Answer

$$0.0181\ 	ext{M/s}$$

Question 4

Which experimental technique would be most appropriate for continuously monitoring the concentration of a colored reactant in solution during a reaction?

Accepted Answer

Spectrophotometry

Question 5

For the reaction $$2	ext{NO}(g) + 	ext{O}_2(g) ightarrow 2	ext{NO}_2(g)$$, the experimentally determined rate law is $$	ext{Rate} = k[	ext{NO}]^2[	ext{O}_2]. $$What is the overall order of the reaction?

Accepted Answer

Third order

Question 6

If the concentration of a reactant in a first-order reaction is halved, what happens to the rate of the reaction?

Accepted Answer

It is halved.

Question 7

A reaction is found to be second order with respect to $$A. $$Which of the following graphs will yield a straight line?

Accepted Answer

$$1/[A] vs. $$time

Question 8

The half-life of a first-order reaction is 26.4 s. How long will it take for the concentration of the reactant to fall to one-eighth of its initial value?

Accepted Answer

$$79.2\ 	ext{s}$$

Question 9

Which of the following statements about activation energy ($$E_a) is $$correct?

Accepted Answer

Activation energy is the minimum energy required for a reaction to occur.

Question 10

According to the Arrhenius equation $$k = A e$$^{-E_a/(RT)}$$, what effect does increasing temperature have on the rate constant k$?

Accepted Answer

It increases $$k.$$

Question 11

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

Accepted Answer

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

Question 12

Which of the following best explains why powdered solids react faster than blocks of the same substance?

Accepted Answer

Powdered solids have a greater surface area for contact with reactants.

Question 13

Which of the following is a correct statement about catalysts?

Accepted Answer

Catalysts provide an alternative pathway with a lower activation energy.

Question 14

In a reaction mechanism, what is an intermediate?

Accepted Answer

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

Question 15

For a zero-order reaction, which of the following is true about the rate and the concentration of the reactant?

Accepted Answer

The rate is constant and independent of the concentration.

Question 16

Which of the following best describes the effect of a catalyst on a reaction energy diagram?

Accepted Answer

It lowers the activation energy barrier.

Question 17

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

Accepted Answer

12

Question 18

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

Accepted Answer

Color of the reactants

Question 19

Which of the following statements about the collision theory of chemical kinetics is correct?

Accepted Answer

Only collisions with sufficient energy and proper orientation result in a reaction.

Question 20

In a biological system, which of the following statements about enzymes is correct?

Accepted Answer

Enzymes provide a specific active site that orients the substrate for reaction.

Chemical Kinetics: Rates, Mechanisms, and Factors Affecting Reactions

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