From Atoms to Materials

The chemical formulae are: • hydrogen: H 2 • chlorine: Cl 2 • hydrogen chloride: HCl Extension + NaCl Cl 2 Na Snapshot aqueous solution 水溶液 State symbols In chemical equations, state symbols are usually used to indicate the physical states of substances. State symbol State (s) solid (l) liquid (g) gas (aq) aqueous solution Among these symbols, (aq) means an aqueous solution*, i.e. the substance is dissolved in water. Note that we NEVER write the state of water as (aq); the state symbol for liquid water is (l). For example, the formation of water from hydrogen and oxygen can be written as: 2H 2 (g) + O 2 (g) 2H 2 O(l) In the above chemical equation, hydrogen and oxygen are in gas state, while water is in liquid state. We can write a chemical equation to represent a chemical reaction. Now let’s write balanced chemical equations for the following reactions: (a) Formation of sodium chloride from sodium and chlorine (b) Formation of hydrogen chloride from hydrogen and chlorine 57 13 From Atoms to Materials © 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