From Atoms to Materials

matter chemical property 化學性質 mixtures (impure substances) pure substances compounds elements • Matter can be classified as below: • When we examine the physical properties of substances, no new substance is formed . • When we examine the chemical properties of substances, new substances are formed . Chemical properties There are some other properties of iron. When these properties are being examined, there are changes in composition. In other words, new substances are formed. These properties are chemical properties of iron. Two examples are shown in Fig. 13.4. What are the new substances formed in these two cases? Fig. 13.4 Some chemical properties of iron Iron becomes rust when exposed to air and water. The importance of stating the surrounding conditions Both temperature and pressure affect the state or the properties of a substance. Therefore, we need to state the surrounding conditions, e.g. ‘room conditions’, when describing a substance. ‘Room conditions’ refers to 25.0 °C and 1 atm. Snapshot The changes in composition are chemical changes. We shall discuss chemical change in detail in section 13.4. Iron reacts with dilute hydrochloric acid to form iron chloride and hydrogen gas. 8 © 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