Chemical Kinetics Practice Questions & Answers

The rate of reaction is defined as the change in the amount of a reactant or product per unit time. For reactants and products in solution, their molar concentrations are used. Source: OpenStax 12.1 Chemical Reaction Rates.

According to the stoichiometry, 3 moles of $H_2$H2​ are produced for every 2 moles of $NH_3$NH3​ consumed. The rate relationship is:
$-\frac{1}{2}\frac{\Delta[NH_3]}{\Delta t} = \frac{1}{3}\frac{\Delta[H_2]}{\Delta t}$−21​ΔtΔ[NH3​]​=31​ΔtΔ[H2​]​
Given the rate of decomposition (positive value) is $2.0 \times 10^{-6}$2.0×10−6, the rate of $H_2$H2​ production is $\frac{3}{2} \times (2.0 \times 10^{-6}) = 3.0 \times 10^{-6} \text{ M/s}$23​×(2.0×10−6)=3.0×10−6 M/s. Source: OpenStax 12.1 Relative Rates of Reaction.

The instantaneous rate at any time $t​$t​ is given by the negative of the slope of a straight line that is tangent to the concentration-time curve at that time. Source: OpenStax 12.1 Chemical Reaction Rates.

Since the reactant concentration decreases as the reaction proceeds, $\Delta[A]$Δ[A] is a negative quantity. Reaction rates are, by convention, positive quantities, so the negative change is multiplied by $-1$−1. Source: OpenStax 12.1 Chemical Reaction Rates.

The five factors listed are: chemical nature, state of subdivision (physical state), temperature, concentration, and the presence of a catalyst. Molar mass of the product is not a primary factor affecting rate. Source: OpenStax 12.2 Factors Affecting Reaction Rates.

Compared with large solid particles, the rate for smaller particles (powder) is greater because the surface area in contact with the other reactant phase is significantly greater. Source: OpenStax 12.2 The Physical States of the Reactants.

For many chemical processes, reaction rates are approximately doubled when the temperature is raised by $10^\circ\text{C}$10∘C. Source: OpenStax 12.2 Temperature of the Reactants.

Collision theory explains that with an increase in concentration, the chances for collisions between molecules are increased because there are more molecules per unit volume. More collisions mean a faster reaction rate. Source: OpenStax 12.5 Collision Theory (referencing 12.2 concepts).

Compare Trial 1 and Trial 2. $[B]$[B] is constant (0.10 M). $[A]$[A] doubles ($0.10 \rightarrow 0.20$0.10→0.20). The rate doubles ($2.0 \rightarrow 4.0$2.0→4.0). Since rate $\propto [A]^1$∝[A]1, the reaction is First order with respect to A. Source: OpenStax 12.3 Method of Initial Rates.

Compare Trial 1 and Trial 3. $[A]$[A] is constant (0.10 M). $[B]$[B] doubles ($0.10 \rightarrow 0.20$0.10→0.20). The rate remains unchanged ($2.0 \times 10^{-3}$2.0×10−3). Since the rate is independent of $[B]$[B], the reaction is Zero order with respect to B. Source: OpenStax 12.3 Method of Initial Rates.