To balance an unbalanced equation, you need to add numbers to the left of one or more formulae. Here is one way to work out how to do this for the reaction between nitrogen and hydrogen.
|Check to see if there are equal numbers of atoms of each element on both sides. Here there aren’t.||N2 + H2 → NH3|
|There are two nitrogen atoms on the left but only one on the right, so a big 2 is added to the left of the NH3.||N2 + H2 → 2NH3|
|There are two hydrogen atoms on the left but (2 × 3) = 6 on the right, so a big 3 is placed in front of the H2.||N2 + 3H2 → 2NH3|
|Check to see if there are equal numbers of each element of both sides. There are.||(two nitrogen atoms and six hydrogen atoms)|
|Add the state symbols if they are requested.||N2(g) + 3H2(g) → 2NH3(g)|
Balanced equations often include state symbols in brackets after each formula. They show the physical state of that substance.
An aqueous solution forms when a substance dissolves in water.
State symbols are useful because they show what a substance is like. For example:
Sodium metal reacts with water to form sodium hydroxide solution and hydrogen gas. Write a balanced equation for the reaction, including state symbols.
2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g) or
Na(s) + H2O(l) → NaOH(aq) + ½H2(g)