1. Introduction

Concentration Dependent Term of Rate Equation

• If a single rate law is sufficient to monitor the progress of a reaction, it is called a ‘single reaction’. If more than one rate law is required to monitor the composition of all components participating in reaction, then we have ‘multiple reactions’.

• Reaction in which the rate law and stoichiometric equation have a direct correspondence is called an elementary reaction. For example, \[\begin{align*} 1 &\qquad A + B & \rightarrow R \qquad -r_A &= kC_AC_B \\ 2 &\qquad A + 2 B & \rightarrow R \qquad -r_A &= kC_AC_B^2 \\ 3 &\qquad \qquad 2A & \rightarrow R \qquad -r_A &= kC_A^2\end{align*}\]

• Certain reactions that do not hold any correspondence with the respective stoichiometry are called non-elementary reactions. For example, \[\begin{align*} 1 &\qquad A + B &\rightarrow R \qquad -r_A &= kC_A^2 \\ 2 &\qquad \qquad A &\rightarrow R \qquad -r_A &= \frac{k_1C_A}{1+k_2C_A}\end{align*}\]