👇 Frequently asked in IGCSE Chemistry exams are questions on balancing chemical equations. 👇
When you are balancing chemical equations,
🚨The number of atoms of each element should be the same on each side of the equation 🚨
Example 1
Balance the equation for the reaction between sodium and water.
Step 1. Identify the reactants and products of the reaction, and write the word equation.
Reactants: sodium and water
Products: sodium hydroxide and hydrogen gas
Word equation:
sodium + water → sodium hydroxide + hydrogen
Step 2. Write an unbalanced chemical equation by finding out the molecular formula for each substance.
Na + H2O → NaOH + H2
Step 3. Balance the chemical equation by making the number of atoms of each element on each side of the equation equal.
᛫ Sodium: There is one sodium atom on the left and one on the right, so it is balanced.
᛫ Hydrogen: There are two hydrogen atoms on the left and three on the right, so H2 should be (1/2)H2.
Na + H2O → NaOH + (1/2)H2
To keep the coefficients in the simplest whole number ratio, multiply all the coefficients by 2.
2Na + 2H2O → 2NaOH + H2
᛫ Oxygen: There are two oxygen atoms on the left and two on the right, so it is balanced.
Step 4. Make sure the equation is balanced by comparing the number of atoms of each element.
Example 2
Sodium sulfate can be made from sodium hydroxide and sulfuric acid. Balance the equation for the reaction between sodium hydroxide and sulfuric acid.
Step 1. Identify the reactants and products of the reaction, and write the word equation.
Reactants: sodium hydroxide and sulfuric acid
Products: sodium sulfate and water
Word equation:
sodium hydroxide + sulfuric acid → sodium sulfate + water
Step 2. Write an unbalanced chemical equation by finding out the molecular formula for each substance.
NaOH + H2SO4 → Na2SO4 + H2O
Step 3. Balance the chemical equation by making the number of atoms of each element on each side of the equation equal.
᛫ Sodium: There is one sodium atom on the left and two on the right, so NaOH should be 2NaOH.
2NaOH + H2SO4 → Na2SO4 + H2O
᛫ Sulfur: There is one sulfur atom on the left and on the right, so it is balanced.
᛫ Oxygen: There are six oxygen atoms on the left and five on the right, so H2O should be 2H2O.
2NaOH + H2SO4 → Na2SO4 + 2H2O
᛫ Hydrogen: There are four hydrogen atoms on the left and on the right, so it is balanced.
Step 4. Make sure the equation is balanced by comparing the number of atoms of each element.
Example 3
Iron(III) oxide can be reduced by carbon. Write a balanced equation for this reaction.
Step 1. Identify the reactants and products of the reaction, and write the word equation.
Reactants: iron(III) oxide and carbon
Products: iron and carbon dioxide
Word equation:
iron(III) oxide + carbon → iron + carbon dioxide
Step 2. Write an unbalanced chemical equation by finding out the molecular formula for each substance.
Fe2O3 + C → Fe + CO2
Step 3. Balance the chemical equation by making the number of atoms of each element on each side of the equation equal.
᛫ Iron: There are two irons on the left and one iron on the right, so Fe should be 2Fe.
Fe2O3 + C → 2Fe + CO2
᛫ Oxygen: There are three oxygen atoms on the left and two oxygen atoms on the right, so CO2 should be (3/2)CO2.
Fe2O3 + C → 2Fe + (3/2)CO2
To keep the coefficients in the simplest whole number ratio, we multiply all the coefficients by 2.
2Fe2O3 + 2C → 4Fe + 3CO2
᛫ Carbon: There are two carbon atoms on the left and three carbon atoms on the right, so 2C should become 3C.
2Fe2O3 + 3C → 4Fe + 3CO2
Step 4. Make sure the equation is balanced by comparing the number of atoms of each element.
