Equations - higher

Specified formulae

You should be able to recall the formulae of certain substances.

Formulae of substances

Balancing equations

You should be able to write balanced equations if you are given the name or formulae of the reactants and products.

Example

Write the balanced equation for the reaction between calcium and water to produce calcium hydroxide and hydrogen.

Step 1

Write the formulae for each substance:

Ca + H₂O    →    Ca(OH)₂ + H₂

Step 2

Check for one unbalanced element, for example, O. Adjust the number of each atom or molecule needed, but never change a formula. We need two Os on each side:

Ca + 2H₂O    →    Ca(OH)₂ + H₂

Step 3

Check for another unbalanced element. In this example, the equation is now balanced.

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