Question

in a third experiment, 0.10 g samples of mg(s) are placed in excess hcl(aq) of various concentrations: 0.050 m, 0.10 m, 0.25 m, and 0.50 m. the reactions are run in successive order from 0.050 m to 0.50 m, and the time required for each reaction to go to completion is recorded. as the concentration of hcl(aq) increases from 0.050 m to 0.50 m, which of the following is the expected result?
a the reaction time increases, and the rate of the reaction decreases.
b the reaction time decreases, and the rate of the reaction increases.
c both the reaction time and the rate of the reaction increase.
d both the reaction time and the rate of the reaction decrease.

Explanation:

The reaction is between Mg(s) and HCl(aq). Reaction rate is proportional to reactant concentration (HCl here). As HCl concentration increases, more frequent collisions occur, so reaction rate increases. A faster reaction means less time to complete (reaction time decreases). So when [HCl] goes from 0.050 M to 0.50 M (increasing), reaction time decreases and rate increases, matching option B.

Answer:

B. The reaction time decreases, and the rate of the reaction increases.