Chemical Equations

Chemical equation = chemical recipe


Click to see a simple explanation of what information a chemical equation tells us.

A chemical equation describes the ingredients used during a chemical reaction and the products formed. It is, if you like, similar to a recipe. The ingredients or reactants appear on the left of the equation while the products appear on the right. Reactants are always used up during a chemical reaction while the products increase in quantity. Lets look at some examples.

Hydrogen peroxide breaks down to form oxygen gas and water. The word equation for this reaction is shown below.
Hydrogen peroxide ==> oxygen gas + water
Notice how the reactant, which in this case is hydrogen peroxide, is on the left of the arrow while the products, oxygen gas and water, are on the right. Hydrogen peoxide is used up during the reaction while oxygen gas and water increase.

Methane burns to form carbon dioxide and water. The word equation for this reaction is shown below. Note that when a substance burns, it is actually reacting with oxygen. So oxygen must appear on the left side of the equation as a reactant even though it is not stated in the description above.
Methane + oxygen ==> carbon dioxide + water.

Write the word equations for the following chemical reactions.

a) Magnesium burns in oxygen to form a white powder known as magnesium oxide. Solution

b) Hydrogen and oxygen gases react to form water.

c) Sugar reacts with oxygen in our body to produce carbon dioxide and water.

d) Zinc metal and hydrochloric acid react together to produce hydrogen gas and zinc chloride.

e) Some microorganisms, such as yeast, convert sugar into alcohol and carbon dioxide.

f) Plants use carbon dioxide, water and energy from the Sun to produce sugar and oxygen in a process called photosynthesis. Note that sunlight is an essential ingredient and must be included on the left of the equation.

g) Two clear solutions of copper nitrate and sodium carbonate are are mixed to form solid copper carbonate and the soluble salt known as sodium nitrate.

h) Magnesium sulfate and hydrogen gas are produced when magnesium metal is placed in a solution of sulfuric acid. Solution

i) What substance/s decrease during the chemical reaction represented by the word equation below?
Iron metal + oxygen gas ==> rust.

j) Carbon dioxide gas, water and heat energy are produced when wood burns. (Note that heat energy is produced and must appear on the right of the equation).

k) Hydrogen gas and a salt are produced when an acid is poured onto a metal.

Scientists use a special way of writing to describe what happens in a chemical reaction. They describe a chemical reaction by writing a chemical equation using symbols to represent the atoms taking part.
Before you continue, refresh yourself with chemical symbols and chemical formulae