All substances are made up of tiny particles that are constantly in motion. For a chemical reaction to occur, these particles must collide with each other.
However, the rate at which a chemical reaction occurs is not always the same. It depends on a number of factors that can affect whether the reacting particles collide with enough energy to initiate the reaction. These factors are:
We can look at the rate of a chemical reaction in two different ways:
1. How quickly a product forms. To calculate this, we use the equation:
2. How quickly a reactant is used up. To calculate this, we use the equation:
There are three main ways we can measure the rate of a chemical reaction:
We can measure the change in mass of a reactant or product during a chemical reaction. Although, it is easier to measure a product forming than a reactant disappearing.
This method might not be suitable for gases with a small relative formula mass (Mr), as the change in mass could be too small.
We can measure the volume of gas given off using a gas syringe or an upside-down measuring cylinder.
The rate is usually measured in cubic centimetres per second (cm³/s) or cubic centimetres per minute (cm³/min).
We can place the reaction container on top of a black cross and measure the time taken for the mixture to become cloudy. The precipitate formed will cloud the mixture, which prevents the cross from being seen.
However, this method can be subjective, as different individuals might record varying times, disagreeing on the exact moment the solution turns cloudy.