in an experiment, a student wants to increase the rate of a reaction that involves gases. which change to…

Brief Explanations:

According to the ideal - gas law and reaction - rate principles, for gas - phase reactions, decreasing the volume increases the pressure (since $P=\frac{nRT}{V}$, when $V$ decreases and $n$, $R$, $T$ are constant, $P$ increases). Also, decreasing the volume increases the concentration of gas molecules (concentration $c = \frac{n}{V}$, when $V$ decreases and $n$ is constant, $c$ increases). Higher concentration and higher pressure lead to more frequent collisions between gas molecules, thus increasing the reaction rate.

Answer:

Decrease the volume to increase pressure and to increase concentration.