Reactivity 2.2—How fast? The rate of chemical change: Practice Questions

Which change will result in a decrease in the initial rate of reaction between marble chips and dilute hydrochloric acid?

If the rate of a reaction increases by a factor of 9 when the concentration of a reactant is tripled, what is the order of reaction with respect to that reactant?

A proposed mechanism for the reaction \(2NO_2(g) + F_2(g) \rightarrow 2NO_2F(g)\) is:
1. \(NO_2 + F_2 \rightarrow NO_2F + F\) (slow)
2. \(NO_2 + F \rightarrow NO_2F\) (fast)
Which of the following statements is incorrect regarding this mechanism?

Which statement best describes the effect of a catalyst on a chemical reaction?

The reaction \(A + B \rightarrow C\) is found to be zero-order with respect to \(B\). If the concentration of \(B\) is tripled while all other conditions remain constant, what happens to the rate of the reaction?

For the reaction \(2A(g) + B(g) \rightarrow C(g) + 3D(g)\), if the concentration of B decreases at an average rate of \(0.050 \, mol \, dm^{-3} \, s^{-1}\), calculate the average rate of formation of D during the same period.

The rate constant, \(k\), for a reaction is observed to increase significantly with an increase in temperature. Using the Arrhenius equation, explain this observation and discuss the role of activation energy in this phenomenon. Additionally, describe how a catalyst influences the activation energy and consequently the rate constant.

How does increasing the surface area of a solid reactant affect the rate of a chemical reaction?

The reaction between zinc metal and hydrochloric acid produces hydrogen gas:

$$Zn(s) + 2HCl(aq) \rightarrow ZnCl_2(aq) + H_2(g)$$

a) Explain how increasing the concentration of hydrochloric acid affects the rate of reaction, referring to collision theory.

b) Explain how increasing the temperature of the reaction mixture affects the rate of reaction, referring to collision theory and activation energy.

The decomposition of dinitrogen pentoxide, \(N_2O_5\), is a first-order reaction described by the equation:

$$2N_2O_5(g) \rightarrow 4NO_2(g) + O_2(g)$$

At a certain temperature, the rate constant for this reaction is \(k = 6.2 \times 10^{-4} \text{ s}^{-1}\).

a) What is the half-life of \(N_2O_5\) at this temperature? Give your answer in minutes.

b) If the initial concentration of \(N_2O_5\) is \(0.50 \text{ mol dm}^{-3}\), what will be the concentration of \(N_2O_5\) after 30 minutes?

c) Sketch a graph showing how the concentration of \(N_2O_5\) changes with time for this reaction, indicating the half-life. No numerical values are required on the axes, but the shape should be correct and the half-life clearly marked.