The reaction rate $r_i$ is defined as the number of moles consumed or generated per unit of time and reaction mixture volume. \begin{equation} r_i=\frac{1}{V}\frac{dN_i}{dt} \end{equation}

In many chemical reactions, the reaction rate can be expressed as the product of a temperature-dependent factor (kinetic constant) and another factor dependent on the concentrations of reactants.

Consider the reaction $aA+bB\rightarrow cC +dD$, the rate is given by $(-r_A)=-\frac{dc_A}{dt}=kc_A^{\alpha}c_B^{\beta}$, where $\alpha$ and $\beta$ are the partial orders with respect to reactants A and B. The sum of both partial orders gives the overall or global order of the reaction.

Factors Affecting Reaction Rate: Several factors can influence the rate of a reaction, including the concentration of reactants, temperature, pressure, the presence of catalysts, and the surface area in heterogeneous reactions.

It is important to note that the reaction rate is specific to each chemical reaction and may vary under different conditions. Determining the reaction rate is essential for understanding and controlling chemical processes in various contexts, from laboratories to industrial applications.