Chemical equations
Francine Taylor-Campbell, Contributor

Students from Bridgeport High School show the certificates they received at the Bridgeport High School's 28th anniversary on Friday, September 29. - Photo by Anthony Minott

We will pause and consider the topic of Chemical Equations, writing and balancing them.

First of all, 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 exercises.

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

Na2 CO3 (s) + HCl (aq) __________ NaCl + 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.

Na2 CO3 (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) __________ Na3 PO4 (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 react to give calcium chloride, water and ammonia.

In the next series of lessons we will be attempting questions on all the topics previously covered.

Francine Taylor-Campbell is an independent contributor.