Question

8. Classify each of the following changes as physical or chemical: (a) coal burning (b) ice melting (c) mixing chocolate syrup with milk (d) explosion of a firecracker (e) magnetizing of a screwdriver

Answer 1

Answer:

(a) coal burning: chemical change

(b) ice melting: physical change

(c) mixing chocolate syrup with milk : physical change

(d) explosion of a firecracker: chemical change

(e) magnetizing of a screwdriver: physical change

Explanation:

A physical change changes the physical form or the appearance or the property of the substance, but the chemical composition of the matter remains the same. Such a change is reversible in nature.  

Whereas; a chemical change involves a chemical reaction, resulting in the change in the chemical composition of the matter. A chemical change results in the formation of a new substance and is generally irreversible in nature.

(a) coal burning: It is a chemical change because the combustion of coal changes its chemical composition. When coal (carbon) is burned carbon dioxide is released. Irreversible in nature

$C(s) + O_{2}(g)\rightarrow CO_{2}(g)$

(b) ice melting: It is a physical change because ice the solid phase of water melts to get converted to the liquid phase of water only and no change in the chemical composition is seen.

$H_{2}O(s) \overset{\Delta }{\rightarrow} H_{2}O(l)$

(c) mixing chocolate syrup with milk : It is a physical change because on dissolving chocolate syrup in milk, only the color of the milk changes, therefore there is change in the property. As, it involves mixing of two miscible liquids and does not involve any change in the chemical composition of either of the two liquids.

(d) explosion of a firecracker: it is a chemical process, as it involves combustion of an explosive material to produce carbon dioxide, carbon monoxide and water vapour. It is a chemical change because it involves change in the chemical composition. Irreversible in nature

(e) magnetizing of a screwdriver: It is physical change because on magnetization only the magnetic property of the screwdriver changes AND there is no change in the chemical composition of the matter.