Chemistry 9701 · AS & A Level · Reaction kinetics

Reaction kinetics — practice question

$\text{Na}_2\text{S}_2\text{O}_3$ reacts with dilute $\text{HCl}$ and produces a pale yellow precipitate. When $1\ \text{cm}^3$ of $0.1\ \text{mol dm}^{-3}\ \text{HCl}$ is added to $10\ \text{cm}^3$ of $0.02\ \text{mol dm}^{-3}\ \text{Na}_2\text{S}_2\text{O}_3$, the precipitate appears slowly. If the test is done again using $1\ \text{cm}^3$ of $0.1\ \text{mol dm}^{-3}\ \text{HCl}$ and $10\ \text{cm}^3$ of $0.05\ \text{mol dm}^{-3}\ \text{Na}_2\text{S}_2\text{O}_3$, the precipitate appears more rapidly. What accounts for this?

  • AThe activation energy of the reaction is lower when $0.05\ \text{mol dm}^{-3}\ \text{Na}_2\text{S}_2\text{O}_3$ is used.
  • BThe reaction proceeds by a different pathway when $0.05\ \text{mol dm}^{-3}\ \text{Na}_2\text{S}_2\text{O}_3$ is used.
  • CThe collisions between reactant particles are more violent when $0.05\ \text{mol dm}^{-3}\ \text{Na}_2\text{S}_2\text{O}_3$ is used.
  • DThe reactant particles collide more frequently when $0.05\ \text{mol dm}^{-3}\ \text{Na}_2\text{S}_2\text{O}_3$ is used.

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