Four steps to writing equations:
- Write the equation in words
- Write the equation in symbols. Check that you are using the correct formulae.
- Check that the equation is balanced. Balancing means that you have the same number of atom on one side as you do on the other. The reason for balancing is because atoms are not lost or created during a reaction. Remember when you balance you multiply the whole formulae whether its an element or molecule - you do not change its formulae.
- Add state symbols.
Magnesium burns in oxygen to produce magnesium oxide.
Because oxygen has two atoms on the left, we multiply by 2 the MgO so that we now have 2 oxygen atoms on the right.
However we now have two magnesium atoms on the right, so we need to multiply Mg by 2 on the left to balance.
Hydrogen gas reacts with oxygen gas to form water when a spark is placed in the mixture.
There are two oxygen atoms on the left but only one on the right. Hence we need to multiply the H2O on the right by 2.
This gives us two oxygen atoms on both sides but we are now left with only two hydrogens on the left and four hydrogen atoms on the right. Therefore, we multiply the H2 by 2.