Final answer:
Chemists look at the initial reaction rate at the start of a chemical reaction to determine the rate law, which predicts how a reaction progresses, especially because the rates of forward and reverse reactions change as the reaction heads towards equilibrium.
Step-by-step explanation:
Chemists investigate the initial reaction rate right at the beginning of a chemical reaction to understand how different factors, like reactant concentrations, affect the speed of the reaction. This rate helps in formulating the rate law, which can accurately predict how a reaction progresses over time. As a reaction moves toward equilibrium, the rate of the forward reaction decreases while the rate of the reverse reaction increases until they become equal. Measuring these initial rates for reactions under different conditions allows scientists to determine the reaction orders and the rate constant for the reaction.
The initial reaction rate is measured because, as the reaction progresses, changes in concentrations of reactants and products can make the reaction rate variable, often causing it to slow down. Just like a car's speedometer gives the speed of the vehicle at a specific moment, the initial reaction rate gives the rate of the chemical reaction at 'time zero' when measurements are most reliable and not yet influenced by changing concentrations as the reaction approaches equilibrium.