Rate (Speed) of Reaction

Understanding Reaction Rates

The rate of reaction refers to the speed at which reactants are turned into products in a chemical reaction.
It’s usually measured by how much of a reactant is used up per unit of time or how much of a product is formed per unit of time.

The concentration and pressure, surface area, temperature, and presence of catalysts can all significantly affect the rate of reaction.
As the concentration or pressure of reactants increase, the rate of reaction also generally increases. This is due to the increased frequency of particle collisions.
The surface area of solid reactants can also impact reaction rates. Larger surface areas allow for increased contact between reactant particles, leading to a faster rate of reaction.
Higher temperatures usually increase the rate of reaction by giving the particles more kinetic energy, thus increasing the likelihood of effective collisions.
Catalysts speed up reactions by providing an alternative reaction pathway with a lower activation energy.

There are several methods to measure the rate of a chemical reaction. These often involve changes in key properties such as mass, volume of gas, color, or light absorption.
For example, the rate of a reaction that produces a gas can be measured using a gas syringe to measure the volume of gas produced over time.
Colorimetry, a method based on the changing colour of a reaction mixture, can be employed to follow the course of a reaction.

The Collision Theory states that for a reaction to occur, particles must collide with the correct orientation and sufficient energy, known as the activation energy.
Thus, the rate of reaction depends not only on the number of collisions per second, but also on the proportion of collisions that are successful in bringing about the chemical change.
Understanding the collision theory helps us understand why factors such as concentration, surface area, temperature and the use of catalysts affect the rate of reaction.