Chemical reactions play a vital role in your everyday life. When you take a deep breath, you are providing fuel for a series of chemical reactions that keep you alive. When you place a log on a fire, the chemical reactions keep you warm. Chemical reactions in a car’s engine keep it running. Chemical reactions are also used to create new and useful materials such as fuels, plastics, foods and medicines.

Understanding chemical change

The key difference between a physical change a chemical change is that new substances are produced during chemical change. Your can usually determine that new substances have been produced by observing one or more of the following:

• A permanent color change occurs
• a gas is given off
• a solid precipitate (falls) out of a solutions
• a change in temperature happens or light is produced.

Why are substances different?

There are billions of different substances that make up the universe, and each substance is special in its own way. The unique set of characteristics of each substance is known as its properties.

Water and hydrogen peroxide (bleach) molecules are similar- both are made of oxygen and hydrogen atoms. Despite having similar molecules, these two compounds have very different properties.

Water has two hydrogen atoms and one oxygen atom, and so it has the chemical formula H2O. Hydrogen peroxide has two hydrogen atoms and two oxygen atoms, and so it has the chemical formula H2O2. Despite water and hydrogen peroxide having very similar molecules, water is safe for drinking, bathing whereas hydrogen peroxide is a type of bleach that attacks your eyes, skin and hair and reacts explosively with some metals.

Chemicals reactions

During a chemical change, old substances disappear and new substances form. The only way this can occur is if the atoms in the old substances rearrange to form to form new substances during the change. The process of rearranging atoms to form a new substance is known as a chemical reaction. In a chemical reaction, the old substances are known as the reactants. The new substances that form are referred to as the products.

An example of a simple chemical reaction is the reaction that happens when magnesium is burnt in the air. in this reaction, magnesium metal (Mg) and oxygen gas (O2) are the reactants. Magnesium is a light and soft, silver grey metal and when burns with oxygen it produces large amounts of light and heat. At the end of the chemical reaction, the magnesium metal has gone but a lght grey powder has formed in its palace. This is a new substance called magnesium oxide (MgO). Magnesium oxide is the product of the reaction.