Identify the dependent and independent variables and describe how the rate of reaction changes over time in the provided experiment.

The dependent variable is the quantity that is measured or observed during the experiment.

• The dependent variable is the volume of CO$_2$ gas produced.

The independent variable is the quantity that is intentionally changed by the experimenter to observe its effect.

• The independent variable is the state of division of CaCO$_3$ (or surface area of CaCO$_3$).

The rate of reaction is represented by the gradient of the curve (volume of CO$_2$ vs time).

• During the interval from 20 s to 40 s, the curve is still rising but becoming less steep. Therefore