The Basics of Reaction Rates

Reaction rate refers to how fast or slow a reaction proceeds.
The speed of a reaction is measured by the change in concentration of a reactant or product per unit time.
Reaction rates can change based on the concentration of reactants, temperature, surface area, presence of a catalyst, and the nature of reactants and products.

Rate Equations

The rate equation links the rate of reaction to the concentrations of the reactants.
It’s usually in the form: Rate = k[A]^m[B]^n
In the equation, k is the rate constant, [A] and [B] are the concentrations of the reactants, and m and n are the orders of reaction.
The overall order of a reaction is the sum of the individual orders (m + n).
The rate constant, k, changes with temperature.

Orders of reaction are determined experimentally by observing how the rate changes when the concentration of one reactant is altered, keeping others constant.
Order can be zero, first or second. A zero order reaction doesn’t depend on the concentration of the reactant, a first order reaction depends on the concentration to the power of 1, while a second order reaction depends on the concentration squared.
Zero order: the rate doesn’t change as you change the concentration of the reactant.
First order: the rate doubles as the concentration is doubled.
Second order: the rate quadruples as the concentration is doubled.

The Arrhenius equation links the rate constant (k) to the temperature of the reaction and the activation energy (Ea).
The equation is: k = Ae^(-Ea/RT)
In the equation, A is the pre-exponential factor or frequency factor which is related to the collision frequency of the reactants, Ea is the activation energy, R is the gas constant and T is the Absolute temperature.

A catalyst is a substance that increases the rate of a chemical reaction by providing an alternative reaction pathway with a lower activation energy.
Catalysts remain chemically unchanged by the end of the reaction. They can be reused.
In the reaction between ozone and nitrogen dioxide, the nitrogen dioxide acts as a catalyst and speeds up the rate of reaction.

Understanding reaction rates and the factors that affect them is crucial in understanding how atmospheric ozone is formed and degraded.
Reactions in the ozone layer, like the reaction of ozone with nitrogen dioxide, happen in three steps - initiation, propagation and termination. In each of these steps, reaction rates play a key role.
Knowing and understanding these rates is crucial for modelling ozone loss and for developing effective strategies to protect the ozone layer.