The law of conservation states that no atoms are lost or gained during a chemical reaction. This means that the total number of atoms must remain constant before and after the reaction.
To write a balanced chemical equation, we start by writing the reactants (the substances that react) on the left-hand side of the arrow and the products (the substances that are produced) on the right-hand side.
Next, we make sure that there is the same number of atoms of each element on both sides of the arrow. If not, we add coefficients (numbers in front of the chemical formulas) to balance the equation.
For example, let’s look at the reaction between oxygen (O2) and hydrogen (H2) to form water (H2O):
|Look at the number of atoms of each element on each side to check if they are equal. In this case, they aren’t.||O2 + H2 → H2O|
|As there are two oxygen atoms on the left of the arrow and only one on the right of the arrow, add a coefficient of 2 in front of H2O.||O2 + H2 → 2H2O|
|There are two hydrogen atoms on the left side and four on the right side, so we add a coefficient of 2 in front of H2. After this, the equation is balanced, with two oxygen atoms and four hydrogen atoms on both sides.||O2 + 2H2 → 2H2O|
|If required to do so, add state symbols.||O2 (g) + 2H2 (g) → 2H2O (l)|
Let’s look at another example that involves sulphuric acid (H2SO4) reacting with sodium hydroxide (NaOH).
Balance the equation below and add state symbols.
H2SO4 + NaOH → Na2SO4 + H2O