Question

How do you use the law of conservation of mass to explain why a chemical equation must be balanced?

Answer 1

Conservation of mass states that mass cannot be created or destroyed. Atoms have mass.

Think of a chemical equation as a mathematical one: the arrow is equivalent to an equals (=) sign. What is on one side of the arrow is shown to be equal to what is on the other side of the arrow.

If an equation is unbalanced, you are effectively showing atoms vanishing, or appearing from nowhere. This would violate the law of conservation of mass.

You wouldn't write a maths sum as 2 + 2 = 3, so you can't write a chemical equation as `H_2 + O_2 -> H_2O`