The rate of chemical reactions (the number of molecules reacting per unit time) depends upon the concentration of the reactants. Reactions can be plotted on a Cartesian graph with time as the x-axis and concentration as the y-axis. Since rate is given in units of moles per unit time, the reaction rate at a given point in time is the slope of the graph. The slope is given by the tangent line at that point. The tangent line intersects the graph at exactly one point; each point on the graph has a unique tangent line. This slope gives the instantaneous reaction rate.
Each chemical reaction follows a given rate law. The rate law for a given reaction expresses the rate of the reaction in terms of the concentrations of the reactants. These values are related by the rate constant k . Rate laws take the form of
Important: X, Y, and Z are determined experimentally and are not necessarily the same as the stochiometric coefficients in the overall chemical equation for the reaction. However, the exponents x, y and z are the same as the stochiometric coefficients of the rate limiting step.
