Balanced chemical equations sometimes 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:
If an equation is written by just replacing names with formulae, it may not be balanced. The numbers of atom of each element on the left must be the same as they are on the right. This follows from the law of conservation of mass - the mass of all the atoms must be the same in the reactions and the products.
To balance an unbalanced equation, 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 an equal number of atoms of each element on both sides. There is not.||N2 + H2 → NH3|
|There are two nitrogen atoms on the left but only one on the right, so put a big 2 on the left of the NH3.||N2 + H2 → 2NH3|
|Check again. There are two hydrogen atoms on the left but (2 × 3) = 6 on the right, so put a big 3 in front of the H2.||N2 + 3H2 → 2NH3|
|Check again to see if there are equal numbers of each element on both sides. There is.||(Two nitrogen atoms and six hydrogen atoms)|
|Add the state symbols if asked to do so.||N2(g) + 3H2(g) → 2NH3(g)|