Chemistry 112 Chapter 16

Express the rate of reaction in terms of the change in concentration of each of the reactants and products in the reaction A (g) + 2B (g) → C (g).

- Δ[A]Δt = - 1/2 Δ[B]Δt = Δ[C]Δt

For the reaction aA + bB → cC + dD, the rate law is given by rate = k[A]m[B]n. Match the appropriate definition with each term of the rate law.

k matches Choice, Rate constant Rate constant m, n matches Choice, Reaction orders Reaction orders [A], [B] matches Choice, Reactant concentrations Reactant concentrations

Select the correct statements regarding activation energy and the heat of a reaction. Select all that apply.

ΔH is negative when Ea(fwd) < Ea(rev) A reversible reaction has two activation energies. ΔHrxn = Ea(fwd) - Ea(rev) Reason: Since ΔHrxn = Ea(fwd) - Ea(rev), when Ea(fwd) > Ea(rev), then ΔHrxn > 0 (endothermic)

Write a balanced chemical equation for the reaction that has the following rate equation: Rate = - 1/2Δ[N2O5]/Δt = 1/4Δ[NO2/]Δt = Δ[O2]/ΔtMultiple choice question.

2N2O5 (g) → 4NO2 (g) + O2 (g)

Match the changes in temperature and activation energy (Ea) for a given reaction with their effect on the rate and rate constant of a reaction.

A decrease in Ea leads to matches Choice, an increase in rate. an increase in rate. A decrease in temperature leads to matches Choice, a decrease in rate. a decrease in rate. k increases matches Choice, if temperature increases. if temperature increases. k decreases matches Choice, if Ea increases. if Ea increases.

Which of the following changes would cause an increase in the reaction rate? Select all that apply.

Increasing the concentration of the reactants Increasing the surface area of the reactants

k Rate constant A Frequency factor Ea Activation energy R Universal gas constant T Absolute temperature

Match

Which of the following statements correctly describe how a rate law is determined? Select all that apply.

The rate law is determined by measuring the initial reaction rate for different reactant concentrations.If there is more than one reactant present the reaction orders will usually be determined individually.The value of k can be calculated from a single experiment once the reaction orders are known.

The reaction of acetone with bromine under acidic catalyzed conditions can be represented by the balanced equation CH3COCH3 + Br2 → CH3COCH2Br + H+ + Br-. The rate of disappearance of Br2 was measured for several different concentrations of the various reactants at a certain temperature. The data are summarized in the table below. Given that the rate law is given by rate = k[CH3COCH3][H+], the rate constant at this temperature is equal to ________.

0.0038 M-1⋅s-1 Reason: The concentration of Br2 does not affect the rate as this reactant does not appear in the rate equation. For all reactions, the rate constant is given by k = rate[CH3COCH3][H+]. Using the data from reaction 1: k = 3.8×10−5(0.20×0.050) = 0.0038 M-1⋅s-1.

Select common laboratory methods for determining the rate of a reaction.

Change in pressure over time Spectrometric methods Change in electrical conductivity

Which of the following statements correctly describe chemical kinetics? Select all that apply.

Chemical kinetics measures how fast reactants are converted into products. Chemical kinetics is the study of reaction rates. Chemical kinetics describes chemical reactions using collision theory.

Which of the following statements correctly describe a rate law for a reaction? Select all that apply. (Assume that the reaction is not reversible to any appreciable extent.)

The rate law relates the rate of reaction to the concentrations of the reactants. The rate law includes the rate constant for the reaction.

Which of the following statements correctly describe the transition state of a reaction? Select all that apply.

The transition state species is highly unstable. The transition state only exists at the instant of highest potential energy in the reaction. Reason: The energy required to form the transition state is the activation energy of the reaction. The enthalpy change (ΔH) reflects the difference in energy between the reactants and products.