Cambridge O Level Chemistry · Syllabus 5070 · Stoichiometry
Chemical equation
What is Chemical equation?
A chemical equation represents a reaction using formulae, with the same number of atoms of each element on both sides; the coefficients written in front of each formula give the ratio in which the substances react, and state symbols show the physical state of each species.
This definition is part of the Stoichiometry chapter in Cambridge O Level Chemistry.
Questions students ask about Chemical equation
How do you balance a chemical equation without changing the formulae?
Change only the coefficients, the large numbers written in front of a formula, because they count how many of that substance react. Never change a subscript: the small number inside a formula is part of the substance's identity, so turning \(\mathrm{H_2O}\) into \(\mathrm{H_2O_2}\) balances the oxygen but changes water into hydrogen peroxide. Write the correct formulae first, add state symbols second, adjust coefficients last, then count every element on both sides before you write the answer down.