From Atoms to Materials

13.4 Balancing a chemical equation Skill Trainingg •  If the number before a chemical formula is ‘1’, omit it. That means, you should write O 2 instead of 1 O 2 . ✗ unbalanced ✗ unbalanced ✗ unbalanced ✓ balanced integer 整數 Extension Write an equation using the chemical formulae of the reactants and products. 1 Count the number of O atoms. Left: 2 Right: 1 2 Count the number of H atoms. Left: 2 Right: 4 4 H 2 + O 2 H 2 O H 2 + O 2 H 2 O H 2 + O 2 2 H 2 O H 2 + O 2 2H 2 O 2 H 2 + O 2 2H 2 O •  DO NOT change the chemical formula of any substance, e.g. H 2 + O 2 H 2 O ✗ We cannot change or delete this subscript. To balance the number of O atoms, add 2 in front of H 2 O. 3 To balance the number of H atoms, add 2 in front of H 2 . 5 2 2 4 1 Note that: •  Use the smallest possible integers*, e.g. 4H 2 + 2O 2 4H 2 O ✗ 2H 2 + O 2 2H 2 O ✓ The equation is now balanced! Handling data Simulation Balancing chemical equations Follow these steps to balance a chemical equation. 56 © United Prime Educational Publishing (HK) Limited 2024 All rights reserved; no part of this publication may be reproduced, photocopied, recorded or otherwise, without the prior written permission of the Publisher. Sample