Chem ch 12

Which of the following represents the rate at which ClO₂⁻(aq) is appearing in the reaction below? 2 ClO₂(aq) + 2 OH⁻(aq) → ClO₂⁻(aq) + ClO₃⁻(aq) + H₂O(l)

+∆[ClO₃⁻]/∆t The rate of a reaction is equal to the rate of change of a reactant or product, divided by its coefficient in the balanced equation. Since reactants are disappearing they have negative values and products have positive values. For the given reaction 2 ClO₂(aq) + 2 OH⁻(aq) → ClO₂⁻(aq) + ClO₃⁻(aq) + H₂O(l) the rate can be expressed in terms of any one of the reactants or products as follows: Rate: see WD Both ClO₂⁻ and ClO₃⁻ have positive rates and a coefficient of 1, so See WD can also represent the rate at which ClO₂⁻(aq) is appearing.

For the reaction 2 A + 3 B → 4 D + 5 E, how is the rate of reaction expressed in terms of rate of disappearance of B?

-1/3∆[B]/∆t The rate of a reaction is equal to the rate of change of a reactant or product, divided by its coefficient in the balanced equation, with negative values for reactants because they are disappearing and positive values for products. WD

Given the reaction A + 2 B → 3 C, the rate of appearance of C is also equal to which of the following?

-3/2∆[B]/∆t The rate of a reaction is equal to the rate of change of a reactant or product, divided by its coefficient in the balanced equation. Since reactants are disappearing they have negative values and products have positive values.

Which of the following affects the collision rate of molecules in the gas phase?

All of these affect collision rate The collision rate is affected by speed, mass, and molecular diameter.

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

All of these will decrease the rate of a reaction. The rate of reaction is affected by the concentration of the reactants, the presence of a catalyst, the surface area of the reactants, and the temperature of the reaction. Removing or decreasing each of these would result in a decreased reaction rate.

What is the order of the reaction if A decomposes to B and C with a rate constant of 8.43 × 10⁻⁴ s⁻¹ at a certain temperature?

First You can tell the order of a reaction from the units of the rate constant. The rate constant of this reaction has the units s⁻¹, so it is a first order reaction.

What are the units for the rate constant of a first-order reaction?

In a first order reaction the rate is directly proportional to the concentration of the reactant.

What are the units for the rate constant of a reaction with the rate law, Rate = k[A][B]?

M⁻¹ s⁻¹ The rate of a reaction is expressed in the units M s⁻¹. For the rate law, Rate = k[A][B], rearrange the equation, and add units to see what the units of k must be.

The units for the rate constant for a zero oder reaction are

M･s⁻¹ The units for the rate constant for a zero order reaction are M･s⁻¹. The rate law for a zero order reaction is

Which species has the greatest rate of appearance in the reaction below? 2 H₂S + O₂ → 2 S + 2 H₂O

S and H₂O have identical rates

The reaction rate of a reaction at 60 °C will be greater than at 30°C because

The molecules are moving faster at higher temperatures. This increases the likelihood that they have enough kinetic energy to react.