For a reaction that follows first-order kinetics, the reaction rate is directly proportional to the concentration of one of the reactants. This means that if you increase the concentration of the reactant, the reaction rate will also increase, and if you decrease the concentration, the reaction rate will decrease.Mathematically, this relationship can be represented by the rate law equation:Rate = k[A]where Rate is the reaction rate, k is the rate constant, and [A] is the concentration of the reactant. As you can see from this equation, the reaction rate is directly affected by the concentration of the reactant A. So, varying the concentration of reactants in a first-order reaction will have a direct impact on the reaction rate.