General Chemistry/Reaction Rates

Introduction

Reaction rates of a chemical system provide the underpinnings of many theories in thermodynamics and chemical equilibria. For non-complex reactions, the reaction rate is extremely trivial to deduce; however, should the system become complex one needs to rely on the "complicated rate reaction equation," which is outside the scope of this book.

Rate Equation

Consider an arbitrary chemical reaction:

$\text{mA}+\text{nB}\Rightarrow \text{C}+\text{D}$

The rate at which the products will form from the reactants is given by:

rate = k[A]^m'[B]^n'

Note [A] is raised to the n^'. This means that the rate of the reaction may rely on the molar coefficients of the species A and/or B, but it might not. However, for an elementary reaction, the concentrations of the species A and B are raised to their molar coefficients. This only applies to elementary reactions, which is a very important distinction to make. K, of course, is the rate reaction coefficient which is reaction specific.

Rate Equation Problems

Usually, when working with the non-complex rate equation, we are given experimental data concerning the concentrations of the chemical species and the rate at which the reaction is proceeding after a given time. Using the experimental data, we can formulate a possible rate equation for the proposed reaction. Let us consider the reaction of Sodium with Chlorine to form ordinary table salt (NaCl).

$\text{Na}+\text{Cl}\Rightarrow \text{NaCl}$ to be continued.