Balancing Chemical Equations
GCE O level, Singapore, 2012/P1/Q12

GCE O level, Singapore, 2012/P1/Q12

When heated, two moles of X give one mole of oxygen and two moles of chlorine. What is the molecular formula of X?

A) ClO2 B) Cl2O C) Cl2O2 D) Cl4O2

In chemistry, a chemical equation represents what occurs in a chemical reaction. We can write an equation by using chemical names (in words) or chemical formulae.

An equation is balanced when there is an equal number of atoms of each element on both sides of the equation.

Steps in balancing chemical equation

1. Write down the formulae of the reactants and products.
2. Check the number of atoms of each element on both sides of the equation. If the equation is not balanced, proceed to step 3.
3. Balance the equation by placing numbers in front of the formulae of the substances in the equation. The number ‘1’ is not written.
4. Write down the state symbols in the equation.

Common Example

In this video, we will start off by writing a common chemical equation for the reaction between sodium and chlorine to form sodium chloride.

Then, we will proceed to work out the molecular formula of X in this question.

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Balancing of Chemical Equations – 2012/P1/Q12

Balancing Chemical EquationsGCE O level, Singapore, 2012/P1/Q12