Final answer:
The term that describes the change in the concentration of a reactant divided by the change in time is the reaction rate, which is measured in units such as M/s, M/min, or M/h.
Step-by-step explanation:
The term that describes the change in the concentration of a reactant divided by the change in time of the reaction is the reaction rate. This is typically expressed as the concentration of reactant consumed or the concentration of product formed per unit time, and the units are moles per liter per unit time (M/s, M/min, or M/h).
To measure reaction rates, chemists will initiate a reaction, measure the concentrations at different times, plot these concentrations versus time, and then calculate the rate by finding the slope of the tangent to the concentration vs. time curve at any given point.