From Atoms to Materials

chemical change 化學變化 chemical reaction 化學反應 alkali acid Photosynthesis Glucose and oxygen are produced. Burning of fuel Carbon dioxide and water are produced. Acid-alkali neutralization Salt and water are produced. Snapshot A change of state: melting butter A chemical change is a change that involves chemical properties. Refer to section 13.1 for details on chemical properties. For simplicity, we sometimes say ‘reaction’ to mean ‘chemical reaction’. Changes of state All changes of state are physical changes. As we learnt in Chapter 6, different states of matter are due to different arrangements of particles. No new substance is formed in the process. Fig. 13.20 Some examples of chemical changes On the other hand, when iron is heated with sulphur, a new substance is formed (iron sulphide). It has properties different from those of iron or sulphur. This is an example of a chemical change . All chemical reactions are chemical changes. Some chemical reactions we have learnt are shown below. In each of these chemical reactions, new substances are formed. Can you think of other examples of chemical changes? • During a physical change, no new substance is formed. • During a chemical change, one or more new substances are formed. 50 © 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