A differential rate law refers to the rate at which a chemical reaction occurs with respect to various concentrations of reactants. Rate laws are expressed as formulas for three types of reactions. Zero-order, first-order and second-order reactions have different constants for differential rate laws. Differential rate laws are determined experimentally as the reaction progresses until one reactant is completely consumed.
In a zero-order reaction, the rate of reaction is constant from beginning to end. When the rate (r) is expressed as a constant (k), a zero order reaction is expressed as r=k where the constant (k) is moles per second. Both reactants are used equally to make products.
In a first-order reaction, the rate of reaction is directly proportional to the amount of one of the reactants. The rate constant (k) in this reaction is seconds. The overall formula is r=k[A], where A stands for the concentration of one of the reactants. When the concentration drops, so does the rate of the reaction.
For a second-order reaction, the reaction rate is related to the square of one of the reactants. This equation looks like r=k[A]^2, where the constant (k) is moles per second. When the reactant is used up, the rate of reaction decreases more rapidly than in a first-order reaction.
A mole is the number of atoms in a particular weight of a substance. Reactants are two substances in a chemical reaction that make products as the reaction progresses.