Chapter 14 Homework

Question 1

True or false?
the orders of the reactants in the rate law (m and n in rate = k[A]m [B]n ) are always the same as the stoichiometric coefficients in the balanced reaction (a and b in aA + bB → cC + dD).

Answer 1

false

Question 2

The data below is for a reaction A → B + C. True or false: this reaction is second-order in A.

Answer 2

true

Question 3

Paperclips are made of an aluminum-iron alloy coated with a layer of alumina (aluminum oxide). When a few drops of water are added to a flask containing powdered iodine and a polished, shiny paperclip, a violent reaction occurs, and a purple vapor is given off. When a few drops of water are added to a flask containing powdered iodine and an unpolished paperclip, the same reaction occurs, but at a much slower rate. In both cases, the paperclip is at least partially consumed during the course of the reaction.
True or false: Alumina serves as a catalyst in this reaction.

Answer 3

false

Question 4

What is the molecularity of the reaction 2A → B?

Answer 4

bimolecular

Question 5

Gasoline is a mixture of hydrocarbons of various chain lengths, ranging from 5-carbon chains to 10-carbon chains. One of the hydrocarbons we often hear about is the 8-carbon chain, octane. Octane combusts with oxygen as given by the balanced equation:

2C8H18(g) + 25O2(g) → 16CO2(g) + 18H2O(g)

Recall that you cannot infer the reaction pathway from the balanced equation. It must be derived experimentally. Yet upon reading this balanced equation, it appears unlikely that the combustion of octane occurs in a single step. Why

Answer 5

It would require the simultaneous collision of 27 molecules.

Question 6

The plot of [A] versus time shows that the decomposition reaction of A is what type of reaction?

Answer 6

first-order

Question 7

For the reaction, CO(g) + NO2(g) → CO2(g) + NO(g), if the second, fast step of the proposed two-step mechanism is NO3(g) + CO(g) → NO2(g) + CO2(g), what is the first step of this reaction?

Answer 7

2NO2(g) → NO(g) + NO3(g)

Question 8

Which reaction shown below involves a heterogeneous catalyst?

Answer 8

2NO(g) -Pt(s)-> N2(g) + O2(g)

Question 9

A scientist gathers the following initial rate data
for the reaction of pyridine (C5H5N) with
methyl iodide (CH3I).

Experiment [C5H5N]0, M [CH3I]0, M Initial rate, M/s
1 0.015 0.025 2.810^-2
2 0.025 0.015 2.810^-2

What can you conclude about the rate law from
this information? (Assume that the exponents in
the rate law are whole numbers.)

Answer 9

The overall order of the reaction is an even number.

Question 10

Find the initial concentration of a sucrose solution that has a current concentration of 3.45 g / L after 2 hours and 30 minutes at 25°C. For this reaction at 25°C, k = 4.10 × 10^−2 hr−1.

Answer 10

3.82 g / L

Question 11

The reaction rate of CO(g) + Cl2(g) → COCl2(g)

at 250°C is 1.5 × 10^3 times as fast as its rate at 150°C. What is the activation energy of the reaction?

Answer 11

135 kJ mol −1

Question 12

Which of the following expresses the half-life for a first-order reaction?

Answer 12

t1/2 = ln 2/k

Question 13

The accepted mechanism for the reaction of methane (CH4) and chlorine (Cl2) to produce chloromethane (CH3Cl) is:
slow:
Cl2(g) -> 2Cl(g)

fast:
CH4(g) + Cl(g) -> Ch3(g) + HCl
CH3(g) + Cl2(g) -> CH3Cl(g) + Cl(g)
2Cl(g) -> Cl2(g)

overall:
Ch4(g) + Cl2(g) -> CH4Cl(g) + HCl(g)

Based on this mechanism, what is the rate law for this reaction?

Answer 13

rate = k[Cl2]

Question 14

Nitrogen monoxide reacts with hydrogen gas
according to the following equation:

2NO + 2H2 → N2 + 2H2O

A scientist gathers the following initial rate
data for the reaction:

If the rate constant for this reaction is 490 M −2s−1,
what is the rate law?

Answer 14

rate = (490 M −2s−1 ) • [ NO]2 [H2 ]

Question 15

Given the following reactions, what rate law is predicted by this mechanism?

H2O2(aq) + I-(aq) -> H2O((l) + IO-(aq) (slow)
H2O2(aq) + IO-(aq) -> H2O(l) + O2(g) + I-(aq) (fast)

Answer 15

Rate = k1[H2O2 ] [ I − ]

Question 16

Using the following data for the reaction 2NO2(g) + F2(g) → 2FNO2(g)
what are the values of m, n, and k in the rate law rate = k[ NO2 ]m [ F2 ]n?

Answer 16

m = 1, n = 1, k = 1.6 M −1s−1

Question 17

Hydrogen and oxygen can react to form water. Why then, is it possible to have pure hydrogen and pure oxygen present in a balloon without any reaction occurring at all?

Answer 17

Ea for the reaction is quite high

Question 18

Which of the following describes how the instantaneous reaction rate changes over time during the formation of O2 from the decomposition of N2O5?

Answer 18

The rate decreases to zero as the reaction time increases

Question 19

Which of the following statements best describes the relationship between the rate law and the events at the atomic-molecular level?

Answer 19

The rate law is consistent with what is happening at the atomic-molecular level.