52 A YEAR IN SCIENCE 



Chemical change. Matter may undergo other 

 changes in which it& composition is altered. When a 

 piece of coal is burned, ashes and invisible gases are 

 formed. These are entirely different in composition 

 and properties from the original coal. Iron when 

 exposed to moist air is gradually changed into rust. 

 This rust is not the same as the iron. If sugar is cov- 

 ered with sulphuric acid and slowly heated, a black 

 substance is formed which is neither sweet nor soluble 

 in water. Such changes are evidently quite different 

 from the physical changes just described, for in them 

 new substances are formed in place of the ones under- 

 going change. Changes of this kind are called 

 chemical changes. Chemical changes are those which 

 involve a change in the composition of substances and 

 result in the formation of new substances. 



Questions 



1. What is a physical change? 



2. Name three physical changes. 



3. How does a chemical change differ from a 

 physical change? 



4. Name three chemical changes. 



5. Classify the following as examples of physical 

 or chemical changes : 



a. Ice to water. 



b. Hydrochloric acid on marble. 



c. Burning of wood. 



d. Carbon dioxide in lime water. 



e. Electric current passing over a wire. 



