Butane, C4H10\mathrm{C_{4}H_{10}}C4H10, burns completely in oxygen to form carbon dioxide and water.
C4H10+O2→CO2+H2O\mathrm{C_{4}H_{10} + O_{2} \rightarrow CO_{2} + H_{2}O}C4H10+O2→CO2+H2O (not balanced)
The equation is balanced using the smallest whole numbers.
What number goes in front of O2\mathrm{O_{2}}O2?
6.5
7
13
26
55 exam-style questions on OCR GCSE Chemistry 3.1 Introducing chemical reactions, covering 3.1.1 Writing formulae and balanced chemical equations, 3.1.2 Formulae of compounds from ions, and state symbols, 3.1.3 Conservation of mass and observed changes in mass, 3.1.4 Half equations and balanced ionic equations, 3.1.5 The mole and the Avogadro constant, and 3.1.6 Stoichiometry, limiting reactants and reacting masses. Each one has a worked solution and a mark scheme showing where the marks go.