In a first-order chemical reaction, the rate of the reaction is directly proportional to the concentration of one of the reactants. This means that if the concentration of the reactant is increased, the rate of the reaction will also increase, and if the concentration is decreased, the rate of the reaction will decrease. Mathematically, this relationship can be represented as:Rate = k[A]^1where Rate is the reaction rate, k is the rate constant, and [A] is the concentration of the reactant A.Experimental evidence to support this relationship can be obtained by conducting a series of experiments in which the concentration of the reactant is varied while keeping other factors such as temperature and pressure constant. By measuring the rate of the reaction at different concentrations, a direct relationship between the concentration and the reaction rate can be established.For example, consider the first-order reaction of the decomposition of hydrogen peroxide H2O2 into water and oxygen:2H2O2 aq 2H2O l + O2 g In an experiment, a chemist could prepare several solutions with different initial concentrations of hydrogen peroxide and measure the rate of oxygen gas production over time. The data collected would show that as the concentration of hydrogen peroxide increases, the rate of oxygen production also increases, confirming the first-order relationship between the concentration of the reactant and the reaction rate.In summary, for a first-order chemical reaction, changing the concentration of the reactants directly affects the overall rate of the reaction. Experimental evidence can be obtained by measuring the reaction rate at different concentrations and observing the direct relationship between concentration and reaction rate.