Final answer:
The rate of a reaction can be represented by the time-dependent change in concentration of reactants or products. For a simple reaction A → B, the rate can be expressed as -Δ[A]/Δt for the reactant A or as +Δ[B]/Δt for the product B. These expressions are linked by the reaction's stoichiometry.
Step-by-step explanation:
The rate of a reaction is a measure of how quickly reactants are converted into products in a chemical reaction. This rate can be expressed by the change in concentration of a reactant or product over time. For a reaction A → B, an equivalent expression for the reaction rate in terms of the reactant A would be the negative change in concentration of A over time (-Δ[A]/Δt), as reactants are consumed. Conversely, for the product B, it would be the positive change in concentration of B over time (+Δ[B]/Δt), as products are formed. The relation between these rates is determined by the stoichiometry of the reaction; if one mole of A produces one mole of B, the rates will be equal in magnitude but opposite in sign.
A mathematical representation of the reaction rate, known as a rate expression, defines this change quantitatively. The related rate law shows how this rate depends on the concentration of the reactants and the rate constant.