1. Classify the changes involved in the following processes as physical or
chemical changes:
(a) Photosynthesis
(b) Dissolving sugar in water
(c) Burning of coal
Melting of wax
(e) Beating aluminium to make aluminium foil
(f) Digestion of food
Answers
Answer:
(a) chemical change
(b) physical change
(c) chemical change
(d) physical change
(e) physical change
(f) chemical change
Explanation:
(a) Photosynthesis is the process through which plants convert light energy into chemical energy. Here is the chemical reaction involved: water and carbon dioxide combine to form glucose and oxygen. Since new chemical species are formed, photosynthesis is clearly a chemical change.
(b) We get the white sugar back again. Dissolving sugar in water is a process that is pretty easy to reverse - it is a physical change. Crushing, mixing, dissolving, melting, or boiling something are examples of physical changes.
(c) Burning of coal is a chemical change. When coal is burnt, the chief component, carbon is changed to carbon dioxide. This process cannot be reversed.
(d) The melting of the solid wax to form liquid wax and the evaporation of liquid wax to form wax vapour are physical changes. The burning of the wax vapour is a chemical change.
(e) Beating aluminium to make Aluminium foil is a physical change because with the beating, molding, heat pressing and fabrication process, people can develop their products or aluminium foils with the aluminium sheets.
(f) Food is chemically changed in digestion when new, smaller substances are formed. These chemical changes are examples of chemical digestion. Chemical digestion begins in the mouth when enzymes in saliva begin to break down carbohydrates.
Answer:
(a) chemical change
(b) physical change
(c) chemical change
(d) physical change
(e) physical change
(f) chemical change
Explanation:
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