Calculating Reaction Order

Understanding Reaction order: Reaction order is a term used to describe the relationship between the rate of a chemical reaction and the concentration of the reactants. It can either be zero, first or second order.
Zero-Order Reactions: For these reactions, the rate is constant and does not depend on the concentration of the reactants. It is depicted in the rate equation as rate = k, where ‘k’ is the rate constant. In this case, the concentration of reactants doesn’t affect the rate of reaction.
First-Order Reactions: The rate of these reactions is proportional to the concentration of one of the reactants. The rate equation is given as rate = k[A], with ‘A’ being the concentration of one reactant. This means that if you double the concentration of ‘A’, you will double the reaction rate.
Second-Order Reactions: For these, the rate is proportional to the square of the concentration of one reactant or the product of the concentrations of two reactants. The rate equation is rate = k[A]^2 or rate = k[A][B]. Therefore, if you double the concentration of ‘A’, the reaction rate quadruples.
Determining Reaction Order: Initial rate experiments are conducted to determine the order of the reaction. By observing how the reaction rate changes as the concentration of reactants change, the order can be deciphered.
Use of Rate-Time Graphs: For zero-order reactions, the concentration of the reactant vs time gives a straight line. For first-order reactions, a plot of the natural logarithm of the concentration of the reactant vs time gives a straight line. For second-order reactions, 1 over the concentration of the reactant vs time gives a straight line.
Understanding Half-Life: The half-life of a reaction (t_1/2) is the time taken for the concentration of a reactant to decrease by half. For first-order reactions, the half-life is constant and doesn’t depend on the initial concentration. For zero-order and second-order reactions, the half-life depends on the initial concentration.
Rate Constants: The rate constant ‘k’ is determined experimentally and is unique for every reaction. It is temperature dependent - as temperature increases, ‘k’ typically increases causing the reaction to go faster.+