Q: Which of the following is the correct expression for the average rate of reaction for $$2\ \mathrm{C}_2\mathrm{H}_6\mathrm{OH}(l) + 9\ \mathrm{O}_2(g) \rightarrow 6\ \mathrm{CO}_2(g) + 8\ \mathrm{H}_2\mathrm{O}(g) in $$terms of $$\mathrm{O}_2$$?

$$\text{Average Rate} = -\frac{1}{9} \frac{\Delta [\mathrm{O}_2]}{\Delta t}$$

Question 1

Which of the following best describes the activation energy ($$E_a) in a $$chemical reaction?

Accepted Answer

The minimum energy required for reactant molecules to successfully collide and form products.

Question 2

A reaction has an enthalpy change ($$\Delta H) of$$ $$-50\ \mathrm{kJ}$$ and an activation energy ($$E_a) of$$ $$120\ \mathrm{kJ}. If a $$catalyst lowers the activation energy by $$30\ \mathrm{kJ}$$, what is the new activation energy for the catalyzed reaction?

Accepted Answer

$$90\ \mathrm{kJ}$$

Question 3

Which of the following changes will decrease the rate of a chemical reaction?

Accepted Answer

Decreasing the concentration of the reactants.

Question 4

For the reaction $$2\ \mathrm{NO}(g) + 2\ \mathrm{H}_2(g) \rightarrow \mathrm{N}_2(g) + 2\ \mathrm{H}_2\mathrm{O}(g)$$, if the rate of disappearance of $$\mathrm{NO} is$$ $$0.10\ \mathrm{M/s}$$, what is the rate of formation of $$\mathrm{N}_2$$?

Accepted Answer

$$0.05\ \mathrm{M/s}$$

Question 5

Which of the following statements about catalysts is correct?

Accepted Answer

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

Question 6

According to collision theory, which factor does NOT directly affect the rate of a chemical reaction?

Accepted Answer

Color of the reactants

Question 7

A student measures the concentration of $$\mathrm{H}_2\mathrm{O}_2 in a $$reaction at 25 seconds and 65 seconds. The concentrations are $$0.80\ \mathrm{M}$$ and $$0.60\ \mathrm{M}$$, respectively. What is the average rate of disappearance of $$\mathrm{H}_2\mathrm{O}_2$$ over this interval?

Accepted Answer

$$0.005\ \mathrm{M/s}$$

Question 8

Which of the following energy diagrams represents an exothermic reaction?

Accepted Answer

The products are at a lower energy level than the reactants.

Question 9

For the reaction $$\mathrm{CHCl}_3(g) + \mathrm{Cl}_2(g) \rightarrow \mathrm{CCl}_4(g) + \mathrm{HCl}(g)$$, which graph best represents the concentration of $$\mathrm{CCl}_4 as a $$function of time?

Accepted Answer

A curve increasing and leveling off as time increases.

Question 10

Which of the following will NOT increase the rate of a reaction according to the Arrhenius equation $$k = Ae$$^{-E_a/RT}$$?

Accepted Answer

Decreasing the frequency factor ($$A).$$

Question 11

A reaction has a high activation energy and a negative enthalpy change ($$\Delta H \u003c 0). $$Which of the following is true?

Accepted Answer

The reaction is slow and exothermic.

Question 12

If the rate of decomposition of $$\mathrm{H}_2 is$$ $$1.54\ \mathrm{M/min} in $$the reaction $$2\ \mathrm{NO}(g) + 2\ \mathrm{H}_2(g) \rightarrow \mathrm{N}_2(g) + 2\ \mathrm{H}_2\mathrm{O}(g)$$, what is the rate of formation of $$\mathrm{N}_2 at $$the same time?

Accepted Answer

$$0.77\ \mathrm{M/min}$$

Question 13

Which of the following best explains why increasing the surface area of a solid reactant increases the reaction rate?

Accepted Answer

It increases the number of effective collisions between reactant particles.

Question 14

Which of the following is the correct expression for the average rate of reaction for $$2\ \mathrm{C}_2\mathrm{H}_6\mathrm{OH}(l) + 9\ \mathrm{O}_2(g) \rightarrow 6\ \mathrm{CO}_2(g) + 8\ \mathrm{H}_2\mathrm{O}(g) in $$terms of $$\mathrm{O}_2$$?

Accepted Answer

$$	ext{Average Rate} = -\frac{1}{9} \frac{\Delta [\mathrm{O}_2]}{\Delta t}$$

Question 15

A chemist notices that burning sulfur in pure oxygen produces a much brighter flame than burning it in air. Which factor is primarily responsible for this observation?

Accepted Answer

Increase in concentration of oxygen

Question 16

Which of the following statements about the transition state in a reaction energy diagram is correct?

Accepted Answer

It is the highest energy point along the reaction pathway.

Question 17

For the reaction $$2\ \mathrm{NO}_2(g) \rightarrow 2\ \mathrm{NO}(g) + \mathrm{O}_2(g)$$, if the rate of disappearance of $$\mathrm{NO}_2 is$$ $$0.04\ \mathrm{M/s}$$, what is the rate of appearance of $$\mathrm{O}_2$$?

Accepted Answer

$$0.02\ \mathrm{M/s}$$

Question 18

Which of the following factors does NOT affect the frequency factor ($$A) in $$the Arrhenius equation?

Accepted Answer

Activation energy

Question 19

A reaction is monitored and the following data are collected: At $$t = 0 s$$, $$[A] = 1.00\ \mathrm{M}$$; at $$t = 20 s$$, $$[A] = 0.80\ \mathrm{M}. $$What is the average rate of disappearance of $$A$$ over this interval?

Accepted Answer

$$0.01\ \mathrm{M/s}$$

Chemical Kinetics: Reaction Rates and Factors Affecting Them

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