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What is a chemical reaction?

A chemical reaction produces a chemical change as atoms are rearranged resulting in the production of one or more new substances.

In all chemical reaction there is a conservation of mass. Atoms are neither created nor destroyed.

Chemical reactions  are generally difficult to reverse. eg. Cooking an egg, burning paper or the rusting of iron.

Chemical reactions result in  the production one or more new products with unique properites.

eg. When water is broken down by electrolysis (electricity) hydrogen and oxygen gas are produced. Each of these susbstances have completely different properties compared to water. 

All chemical reactions take the form of

Reactants → Products

The chemicals that react in a reaction are called the reactants.  In the reaction below water is the reactant.

The chemicals that are produced are called the products. In the reaction below hydrogen and oxygen gas are the products.

 Word equations are the simpliest way to represent chemical reactions.

The reactants are written on the left hand side and the products on the right hand side.

The arrow(→) means 'gives' or 'produces'.

Examples of word equations are

  • Hydrogen + Oxygen → Water
  • Sodium + Chlorine → Sodium chloride
  • Zinc + Hydrochloric acid → Zinc chloride + hydrogen gas

In all chemical reactions mass is conserved as reactants are transformed into products by the rearrangement of atoms.