What are the three common temperature scales? Does the size of a degree differ among them?
Solution 21E: Physical process: It is a process where a substance changes its physical appearance but not its composition. It does not form any new substance. For example: evaporation of water. When water evaporates, it changes from liquid state to gaseous state. But it is still in composed of water. Chemical process: It is process where substance is chemically transformed into an another new substance. Therefore the properties will be different from each other. When hydrogen reacts with oxygen, it forms water molecule. (a) rusting of a metal can When iron reacts with air (oxygen) , it undergoes rusting to form Fe O 23nce, in this process, there is a change in chemical composition from reactant to product. Thus, rusting of a metal atom is a chemical process. (b) boiling a cup of water, When water boils, it forms vapour or gas and the process is called vaporization. But the composed substance is remain same and which is water molecule only. There is no change in composition. It only changes its appearance from liquid to gas. Thus boiling of a cup of water is physical process. (c) pulverizing an aspirin Pulverizing is process to make powder. So pulverizing an aspirin does not change its chemical composition. It only changes its physical appearance from solid to powder. Thus pulverizing an aspirin is a physical process. d) digesting a candy bar, Digestion is a chemical change. So digestion a candy bar changes its chemical composition of candy. So, digesting a candy bar is chemical process. (e) exploding of nitroglycerin. Exploding of nitroglycerin gives water vapor, carbon dioxide, nitrogen, and oxygen. So it undergoes chemical change. Therefore, exploding of nitroglycerin is a chemical process.