Chemistry 9701 · AS & A Level · Reaction kinetics

Reaction kinetics — practice question

$\text{Na}_2\text{S}_2\text{O}_3$ reacts with dilute $\text{HCl}$ to form a pale yellow precipitate. When $1\,\text{cm}^3$ of $0.1\,\text{mol dm}^{-3}$ $\text{HCl}$ is mixed with $10\,\text{cm}^3$ of $0.02\,\text{mol dm}^{-3}$ $\text{Na}_2\text{S}_2\text{O}_3$, the precipitate appears slowly. When the experiment is carried out 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. Why does this happen?

  • 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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