Chemical equations
Francine Taylor-Campbell, Contributor

First, an equation is a representation of a reaction. An equation should show the reactants and products taking part in a chemical reaction and should show in what ratio these products combine.

In writing an equation, the first step is to express it in word form. This ensures that all reactants and possible products are accounted for. The second step is to express the word equation in symbols. Here, the correct formula for each reactant and product must be given. The final step is to check that the same number of atoms of a given element or their ions is on each side. When this is done, the equation is said to be balanced. State symbols are also added to the equation.

Now, let us examine the following questions.

1. Write an equation for the reaction between calcium oxide and water.

Water + Calcium oxide ----------------> Calcium hydroxide word

H₂O (l) + CaO (s) ---------------------> Ca(OH)₂ (aq) formula

Checking the number of atoms of each element on both sides

2 H ———— 2 H

2 O ———— 2 O

1 Ca ———- 1 Ca This equation is balanced

2. Write an equation for the reaction between sodium carbonate and hydrochloric acid.

Sodium carbonate + Hydrochloric acid --------------> Sodium chloride + carbon dioxide + water

Na₂CO₃ (s) + HCl (aq) NaCl (aq) + CO₂ (g) + H₂O (l)

Checking both sides

2 Na ———— 1 Na

1 C ————- 1 C

3 O ————- 3 O

1 H ————- 2 H

1 Cl ———— 1 Cl

To balance this equation, 2 can be placed before the Na atom to have 2 Na atoms on both sides.

Na₂CO₃ (s) + HCl (aq) 2NaCl + CO₂ (g) + H₂O (l)

This means we now have 2 Cl on one side and 1 Cl on the other side. Placing a 2 before HCl will balance this.

Na₂CO₃ (s) + 2HCl (aq) 2NaCl + CO₂ (g) + H₂O (l) balanced

3. Write an equation for the reaction between sodium hydroxide and phosphoric acid.

Sodium Hydroxide + Phosphoric acid ----------> Sodium phosphate + water

NaOH (aq) + H₃PO₄ (aq) Na₃PO₄ (aq) + H₂O (l)

Checking sides

1 Na ——— 3 Na

5 O ———- 5 O

4 H ———- 2 H

1 P ———- 1 P

Put 3 in front of NaOH to balance the Na
3NaOH (aq) + H₃PO₄ (aq) --------> Na₃PO₄ (aq) + H₂O (l)

This now creates 6 H ———- 2 H which can be balanced by multiplying the 2 H by 3.

3NaOH (aq) + H₃PO₄ (aq) Na₃PO₄ (aq) + 3H₂O (l) balanced

Now attempt the following.

1. Ammonia reacts with oxygen in air to produce nitrogen and water.
Write a balanced equation for this reaction.

2. Iron III oxide reacts with carbon monoxide to produce iron and carbon dioxide.

3. Calcium hydroxide and ammonium chloride reacts to give calcium chloride, water and ammonia.

Francine Taylor-Campbell teaches at Jamaica College. Send questions and comments to kerry-ann.hepburn@gleanerjm.com