Q: According to Graham’s law, which gas will effuse faster: hydrogen ($$\text{H}_2) or $$oxygen ($$\text{O}_2$$)?

$$\text{H}_2$$ will effuse faster because it is lighter.

Q: A reaction has the rate law $$\text{Rate} = k[\text{NO}_2]^2. $$Which of the following mechanisms is most consistent with this rate law?

A slow step involving two $$\text{NO}_2$$ molecules colliding.

Question 1

A reaction is found to be first order in reactant A. If the initial concentration of A is doubled, what happens to the initial rate of the reaction?

Accepted Answer

The initial rate doubles.

Question 2

Which of the following best explains why a catalyst increases the rate of a chemical reaction?

Accepted Answer

It lowers the activation energy by providing an alternative pathway.

Question 3

For the reaction $$2	ext{O}_3 (g) ightarrow 3	ext{O}_2 (g)$$, if the rate of disappearance of $$	ext{O}_3 is$$ $$0.10\ 	ext{mol/L·s}$$, what is the rate of appearance of $$	ext{O}_2$$?

Accepted Answer

$$0.15\ 	ext{mol/L·s}$$

Question 4

A plot of $$\ln [A]$$ versus time for a reaction yields a straight line with a negative slope. What is the order of the reaction with respect to A?

Accepted Answer

First order

Question 5

The half-life of a first-order reaction is 10 minutes. How long will it take for the concentration of the reactant to decrease to one-eighth of its original value?

Accepted Answer

30 minutes

Question 6

Which of the following statements about the kinetic-molecular theory of gases is NOT correct?

Accepted Answer

Attractive and repulsive forces between gas molecules are significant.

Question 7

A sample of gas has a mass of 2.00 g, occupies 1.00 L at 1.00 atm and 273 K. What is the molar mass of the gas? (Use $$R = 0.0821\ 	ext{L·atm·mol}^{-1}	ext{K}^{-1})$$

Accepted Answer

44.9 g/mol

Question 8

Which of the following best describes the effect of increasing temperature on the rate constant $$k$$ for a chemical reaction?

Accepted Answer

$$k$$ increases as temperature increases.

Question 9

According to Graham’s law, which gas will effuse faster: hydrogen ($$	ext{H}_2) or $$oxygen ($$	ext{O}_2$$)?

Accepted Answer

$$	ext{H}_2$$ will effuse faster because it is lighter.

Question 10

A reaction has the rate law $$	ext{Rate} = k[	ext{NO}_2]^2. $$Which of the following mechanisms is most consistent with this rate law?

Accepted Answer

A slow step involving two $$	ext{NO}_2$$ molecules colliding.

Question 11

Which of the following is a correct expression for the half-life of a second-order reaction with respect to reactant A?

Accepted Answer

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

Question 12

A mixture of gases contains 2.0 mol of $$	ext{N}_2$$, 1.0 mol of $$	ext{O}_2$$, and 1.0 mol of $$	ext{CO}_2 at a $$total pressure of 2.0 atm. What is the partial pressure of $$	ext{O}_2$$?

Accepted Answer

0.5 atm

Question 13

Which of the following best explains why real gases deviate from ideal behavior at high pressures?

Accepted Answer

The volume of the gas molecules becomes significant compared to the container volume.

Question 14

Which of the following is the correct van der Waals equation for real gases?

Accepted Answer

$$\left(P + \dfrac{n^2$a}{V^2$}\right)(V - nb) = nRT$$

Question 15

A reaction is zero order in reactant A. If the initial concentration of A is tripled, what happens to the rate of the reaction?

Accepted Answer

The rate remains the same.

Question 16

Which of the following is NOT a requirement for a plausible reaction mechanism?

Accepted Answer

The mechanism must contain only unimolecular steps.

Question 17

A gas sample is collected over water at 25°C. The total pressure is 755 mmHg, and the vapor pressure of water at 25°C is 23.8 mmHg. What is the partial pressure of the dry gas?

Accepted Answer

731.2 mmHg

Question 18

Which of the following best describes the effect of a heterogeneous catalyst in the hydrogenation of ethene ($$	ext{C}_2	ext{H}_4) $$using a metal surface?

Accepted Answer

The catalyst provides a surface for the reaction, lowering the activation energy.

Question 19

Which of the following is the correct relationship for the rate constant $$k as a $$function of temperature according to the Arrhenius equation?

Accepted Answer

$$k = Ae$$^{-E_a/RT}$$

Chemical Kinetics and Gases: Core Concepts and Applications

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