Rate of reaction Knowledge-Based Practice

Questions

1. 1.

   Which of the following best explains why the instantaneous rate of a typical chemical reaction decreases as the reaction proceeds at constant temperature?

   • A) The activation energy of the reaction progressively increases as products accumulate in the mixture.
   • B) The concentration of reactants decreases, reducing the frequency of collisions between reactant particles.
   • C) The rate constant of the reaction continuously decreases as the quantity of reactants is depleted.
   • D) The enthalpy change of the reaction shifts toward an increasingly unfavorable endothermic value.
2. 2.

   What are the standard units typically used to express the rate of a chemical reaction occurring in a homogeneous solution?

   • A) $\text{mol}\cdot\text{L}\cdot\text{s}^{-1}$
   • B) $\text{mol}\cdot\text{s}^{-1}$
   • C) $\text{mol}\cdot\text{L}^{-1}\cdot\text{s}^{-1}$
   • D) $\text{L}\cdot\text{mol}^{-1}\cdot\text{s}^{-1}$
3. 3.

   Why is a negative sign included in the mathematical definition of the rate of reaction with respect to a disappearing reactant, $-\frac{\Delta [\text{reactant}]}{\Delta t}$?

   • A) To indicate that the chemical process is exothermic and releases thermal energy
   • B) To ensure that the calculated rate of reaction is expressed as a positive value
   • C) To signify that the activation energy barrier decreases as the reaction proceeds
   • D) To represent a shift in the position of dynamic chemical equilibrium toward the left
4. 4.

   How is the instantaneous rate of a chemical reaction determined from a concentration-versus-time graph for a disappearing reactant?

   • A) By calculating the total change in reactant concentration divided by the total elapsed time
   • B) By finding the area under the concentration-versus-time curve over the duration of the reaction
   • C) By recording the reactant concentration present at the exact midpoint of the reaction
   • D) By determining the absolute value of the slope of the tangent line drawn to the curve at that point
5. 5.

   For the reaction $2\text{N}_2\text{O}_5(g) \rightarrow 4\text{NO}_2(g) + \text{O}_2(g)$, what is the relationship between the rate of consumption of $\text{N}_2\text{O}_5$ and the rate of formation of $\text{NO}_2$?

   • A) The rate of formation of $\text{NO}_2$ is half the rate of consumption of $\text{N}_2\text{O}_5$.
   • B) The rate of formation of $\text{NO}_2$ is equal to the rate of consumption of $\text{N}_2\text{O}_5$.
   • C) The rate of formation of $\text{NO}_2$ is twice the rate of consumption of $\text{N}_2\text{O}_5$.
   • D) The rate of formation of $\text{NO}_2$ is four times the rate of consumption of $\text{N}_2\text{O}_5$.

Answers and step-by-step solutions appear after you finish the test.