Q: Which of the following best describes the mathematical definition of reaction rate for a reactant?

$$\text{Rate} = -\frac{\Delta [\text{reactant}]}{\Delta t}$$

Question 1

A lizard is an ectotherm, meaning its body temperature matches its environment. If the temperature drops, what happens to the chemical reactions in the lizard’s body, and why?

Accepted Answer

The reactions slow down because lower temperatures decrease the kinetic energy of molecules.

Question 2

Which of the following best describes the mathematical definition of reaction rate for a reactant?

Accepted Answer

$$	ext{Rate} = -\frac{\Delta [	ext{reactant}]}{\Delta t}$$

Question 3

For the reaction $$2	ext{NOBr}(g) ightarrow 2	ext{NO}(g) + 	ext{Br}_2(l)$$, if 240 g of NOBr decomposes in a 0.200 L flask in 5.0 minutes, what is the average rate of Br$$_2$$ production in M/s? (Molar mass NOBr = 109.91 g/mol)

Accepted Answer

$$0.00545\ 	ext{M/s}$$

Question 4

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

Accepted Answer

Spectrophotometry

Question 5

Which factor does NOT generally increase the rate of a chemical reaction?

Accepted Answer

Decreasing the surface area of a solid reactant

Question 6

The rate law for a reaction is $$	ext{Rate} = k[	ext{A}]^2[	ext{B}]. $$What is the overall order of the reaction?

Accepted Answer

Third order

Question 7

If the rate law for a reaction is $$	ext{Rate} = k[	ext{A}]$$, what will happen to the rate if the concentration of A is tripled?

Accepted Answer

The rate will increase by a factor of 3.

Question 8

A reaction is found to be zero order in reactant A. Which of the following graphs would be linear?

Accepted Answer

$$[A] vs. $$time

Question 9

The half-life of a first-order reaction is given by which equation?

Accepted Answer

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

Question 10

For a second-order reaction $$A ightarrow$$ products, if $$[A]_0 = 0.010\ 	ext{M}$$ and $$k = 1.8\ 	ext{M}^{-1}	ext{s}^{-1}$$, what is the half-life?

Accepted Answer

$$t_{1/2} = \frac{1}{k[A]_0}$$

Question 11

The Arrhenius equation relates the rate constant $$k to $$temperature $$T as $$follows: $$k = Ae$$^{-E_a/RT}$$. What does E_a$ represent?

Accepted Answer

The activation energy required to form the activated complex

Question 12

If a reaction rate doubles when the temperature increases by 10°C, what can you infer about the activation energy?

Accepted Answer

It is high enough that temperature significantly affects the rate.

Question 13

Which of the following statements about catalysts is TRUE?

Accepted Answer

Catalysts provide an alternative pathway with lower activation energy.

Question 14

In a reaction mechanism, what is an intermediate?

Accepted Answer

A species produced in one step and consumed in a later step

Question 15

For the reaction $$2	ext{NO}_2 ightarrow 2	ext{NO} + 	ext{O}_2$$, the experimentally determined rate law is $$	ext{Rate} = k[	ext{NO}_2]^2. $$What does this suggest about the mechanism?

Accepted Answer

The rate-determining step involves two NO$$_2$$ molecules colliding.

Question 16

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 collisions.

Question 17

Which of the following is a correct statement about the orientation factor in collision theory?

Accepted Answer

It is usually less than 1 for complex molecules.

Question 18

Enzymes are biological catalysts. Which statement best describes how enzymes increase reaction rates?

Accepted Answer

They provide a specific orientation and lower the activation energy.

Question 19

A reaction mechanism consists of the following steps:
1. $$A + B_2$ \rightarrow AB + B ($$slow)
2. $$A + B \rightarrow AB ($$fast)
What is the rate law for the overall reaction?

Accepted Answer

$$	ext{Rate} = k[A][B_2$]$$

Chemical Kinetics: Rates, Mechanisms, and Factors Affecting Reactions

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