Question

Explain the following;
(a) A chimney smokes when a fresh fire is started under it.
(b) Small holes are provided at the bottom of the chimney in an oil lamp.
(c) Land becomes warmer than water during the day.

Answer 1

Hint:In order to answer this question, you must be aware about the concept of volatile nature of hydrocarbons, the process of combustion and the radiative heating of land and water.

Complete answer:
(a) When a new fire is started under the chimney, it smokes because the wood or coal contains volatile hydrocarbons at the start of the fire; at that time, the temperature is approximately ${149^0}C$ and after a while, when the hydrocarbons evaporate, there is no smoke.

(b) Small holes are provided at the bottom of the chimney in oil lamps so that plenty of oxygen can reach the flame and aid in combustion. Without oxygen, combustion cannot occur.

(c) The surface heats up during the day and cools down at night. Because land heats faster than water, solar heating of the Earth's surface is uneven, causing air above land to warm, expand, and rise overland while cooling and sinking over cooler water surfaces. Hence, land becomes warmer than water during the day.

Note:Combustion is a chemical process in which a substance reacts rapidly with oxygen and gives off heat. During the process of combustion, new chemical substances are created from the fuel and the oxidizer.