Chemical reactions

Assumed perquisite knowledge:

Students understand the difference between a physical change and a chemical change

What is a chemical reaction?

1. A chemical reaction occurs when substances combine or breakdown to produce something NEW.
2. A chemical reaction is accompanied by a chemical change. eg. A permanent change in color or the production of a gas.

   Chemical changes indicate that something new has been produced. eg. The permanent color change produced as bread is toasted in a toaster or the smoke from a burning match.

3. Chemical reactions are generally difficult to reverse. eg. Turning a slice of toast into a slice of fresh bread.

The chemicals that react are called the reactants.

The new materials that are produced are called the products.

A chemical reaction can be shown by the use of a word equation. The means 'give or produce'

Reactants   Products

chemicals that react chemicals that are produced

Examples of chemical reactions

1. Hydrogen + oxygen   water

 H ₂   + O₂   2H ₂ O

2. Hydrogen peroxide water + oxygen

2H ₂ O₂    2H₂O + O₂

3. Magnesium + oxygen magnesium oxide

2Mg + O₂ 2MgO

4. Sodium chloride sodium + chlorine

 2NaCl 2Na + Cl₂