Question 1

Consider the following reaction for production of ammonia via the Haber process: 3H ₂+ N ₂→ 2NH ₃. Which of the following expressions best illustrates the rate of reaction?

Accepted Answer

The rate of reaction is expressed as the change in concentration of a product divided by the stoichiometric coefficient and time. For NH₃, it is Δ [NH₃] / 2 Δ t.

Question 2

The rate constant "k" will vary with changes in concentration of first order reactants.

Accepted Answer

The rate constant "k" for a first-order reaction is independent of the concentration of reactants; it only changes with temperature or the presence of a catalyst.

Question 3

A reaction mechanism is a collection of elementary steps.

Accepted Answer

This statement is true. A reaction mechanism is a step-by-step description of the elementary steps that occur during a chemical reaction. It outlines the sequence of bond-breaking and bond-forming steps that lead to the overall chemical transformation.

Question 4

The rate of a reaction depends on the concentration of the reactants.

Accepted Answer

The rate of a chemical reaction is often dependent on the concentration of the reactants, as described by the rate law, which relates the rate of reaction to the concentration of reactants raised to a power.

Question 5

Endothermic reactions do not require activation energy.

Accepted Answer

All chemical reactions require some amount of activation energy, including endothermic reactions.

Question 6

For a first-order reaction, a plot of concentration versus time provides a line with a slope equal to − k.

Accepted Answer

For a first-order reaction, a plot of the natural logarithm of concentration versus time provides a straight line with a slope equal to -k.

Question 7

The rate of a reaction may be expressed as the disappearance of reactants with respect to time.

Accepted Answer

The rate of a reaction is defined as the change in concentration of reactants or products per unit time, so it can be expressed as the disappearance of reactants with respect to time.

Question 8

A termolecular step in a reaction mechanism is a step that involves two molecules.

Accepted Answer

A termolecular step involves the collision of three molecules.

Question 9

Stirring a reaction increases the rate of the reaction by raising the activation energy.

Accepted Answer

Stirring a reaction increases the rate by improving the mixing of reactants, not by raising the activation energy.

Question 10

The _____ of a reaction can be obtained by measuring two concentrations of reactants at times separated by a finite difference.

Accepted Answer

The average rate of a reaction is determined by measuring the change in concentration of reactants over a finite time interval.

Question 11

If a reaction is zero order with respect to [B], tripling the concentration of [B] will:

Accepted Answer

In a zero-order reaction, the rate is independent of the concentration of the reactant. Therefore, changing the concentration of [B] will not affect the rate of the reaction.

Question 12

The instantaneous rate of a reaction is determined by the slope of a line tangent to the curve defined by the change in concentration versus time.

Accepted Answer

The instantaneous rate of a reaction is given by the derivative of concentration with respect to time, which is represented by the slope of the tangent line to the concentration vs. time curve at a specific point.

Question 13

For a zero-order reaction, a plot of a reactant concentration versus time is linear.

Accepted Answer

In a zero-order reaction, the rate of reaction is constant and does not depend on the concentration of the reactant, resulting in a linear decrease of reactant concentration over time.

Question 14

O ₃is the most stable allotrope of oxygen.

Accepted Answer

Ozone (O₃) is less stable than dioxygen (O₂) because it is more reactive and tends to decompose back into O₂.

Question 15

According to the differential rate law: rate = k[X]^m[Y]ⁿ. If m = 2 and n = 1, the overall reaction order is:

Accepted Answer

The overall reaction order is the sum of the exponents in the rate law, which is m + n = 2 + 1 = 3.

Question 16

If a reaction is first order with respect to [A], doubling the concentration of [A] will:

Accepted Answer

In a first-order reaction, the rate is directly proportional to the concentration of the reactant. Therefore, doubling the concentration of [A] will double the rate of the reaction.

Question 17

If a reaction is second order with respect to [A], doubling the concentration of [A] will:

Accepted Answer

In a second-order reaction with respect to [A], the rate is proportional to the square of the concentration of [A]. Doubling [A] results in a fourfold increase in the rate (2^2 = 4).

Question 18

The formation of ozone in the stratosphere begins with:

Accepted Answer

The formation of ozone in the stratosphere starts when a UV photon dissociates a diatomic oxygen molecule (O2) into two separate oxygen atoms, which can then react with another O2 molecule to form ozone (O3).

Question 19

For a first order reaction, the plot of concentration of a reactant with respect to time is _____.

Accepted Answer

For a first order reaction, the concentration of a reactant decreases exponentially with time, following the equation [A] = [A]₀e^(-kt), where [A] is the concentration at time t, [A]₀ is the initial concentration, k is the rate constant, and e is the base of the natural logarithm.

Question 20

For a first-order reaction, t_1\2= ln 2\ k

Accepted Answer

This is the equation for the half-life of a first-order reaction, where t1/2 is the time required for the concentration to decrease by half, k is the rate constant, and ln is the natural logarithm function.

Quiz 11: Chemical Kinetics

Consider the following reaction for production of ammonia via the Haber process: 3H 2 + N 2 → 2NH 3 . Which of the following expressions best illustrates the rate of reaction?