Updated: Oct 23, 2019
What’s a chemical reaction? What requirements are there for a chemical reaction to happen? What factors affect the rate of reaction? How can we measure the rate of reaction? In this post I will try to answer these questions. Let’s start!
A chemical reaction is a process which one or more substances, called the reactants, are
converted into one or more substances, the products. Substances are either chemical compounds or elements. A chemical reaction rearranges the constituent atoms of a reactant to create different substances as products. In order for a chemical reaction to happen the reactants need to collide.
The collision of the reactants will provide the kinetic energy needed to form new bonds. Some activation energy is always needed for a chemical reaction to happen.
There are two types of reactions, endothermic and exothermic. Endothermic reactions is when heat energy is converted into chemical energy. This type of reaction is less common. An example is photosynthesis, e.g. a process where plants and other types of organisms convert light energy into chemical energy. An exothermic reaction is when chemical energy is converted into heat energy. This type of reaction is quite common. An example is detonation of nitroglycerin. As a chemical reaction proceeds the reactants get used up and the products are formed.
At any specific time in the course of the reaction the amount (mass, moles, concentration etc.) of the reactants compared to the amount of the beginning of the reaction gives us a measure of how far the reaction has gone. In the same way as a car’s velocity is measured in distance travelled/ time taken so the rate of a chemical reaction is measured as change in reactant or product amount/ time taken. The best definition of the rate of reaction is provided by measuring the change of the concentration of the reactants over time. Rate is change in concentration divided by time.
To find the change in concentration we need to know the volume in which the reaction is
happening. This can only be applied for gases and liquids. The concentration of a reactant is measured in moles per litre (mol dm^-3). The rate of change of concentration can be obtained by doing experiments and measure the change in concentration and the time for a change occuring.
Higher Level Chemistry, Pearson Baccalaureate by Catrin Brown and Mike Ford