The rate of a reaction refers to the speed at which the reaction takes place. The rate of a reaction depends on many variables such as, temperature, concentration of dissolved reactants, pressure of gaseous reactants, surface area of solid reactants, or the presence of a catalyst. In order to measure the rate of a reaction, we must measure the change in amount of a reactant as it is consumed over time, or measure the amount of product formed over time. When you graph the formation of a product, or consumption of a reactant on the y axis, versus the time of reaction on the x-axis, the slope of this function will provide the rate of the reaction.