Question

State for each of the following, whether it is due to evaporation or condensation.
a) Water drops appear on the outer surface of a glass containing cold water.
b) Steam rising from wet clothes while they are ironed.
c) Fog appearing on a cold winter morning.
d) Blackboard dries up after wiping it.
e) Steam rising from a hot girdle when water is sprinkled on it.

Answer 1

Hint: In both the processes of evaporation and condensation, the phase (physical state) of water gets changed depending upon the temperatures.
In evaporation, water is changed to vapour and in condensation, the reverse of evaporation takes place, water vapours are changed into water.

Complete step by step answer:
i) Evaporation is defined as the Conversion of water into water vapours.
When we heat a liquid the force of attraction between its molecules decreases and hence the liquid changes to a gas and evaporates.
This process is endothermic i.e. absorbs heat and hence occurs at a higher temperature.
ii) Condensation: Conversion of water vapour water into liquid.
When a gas is cooled, the force of attraction between its molecules increases, and hence the gas condenses either to a liquid or a solid
This process generally occurs at lower temperature and releases energy
Using this information, we will be answering the given statements option by option.

a) Water drops appear on the outer surface of a glass containing cold water –
Water vapours are always present in the air (due to them, the air is moist and humid) and when they come in contact with a cold surface (here, a cold glass), they condense into water vapour.
Therefore, this is due to the process of condensation.
b) Steam rising from wet clothes while they are ironed-
Wet clothes have water stored on the surface and heat from iron converts these water droplets are into water vapours
Therefore, this is due to the process of evaporation.
 c) Fog appearing on a cold winter morning –
Fog consists of tiny water droplets and these droplets get condensed due to cold weather.
Therefore, this is due to the process of condensation.
d) Blackboard dries up after wiping it –
During the wiping of the blackboard, the blackboard absorbs heat from the surroundings due to which water droplets present on board evaporate.
Therefore, this is due to the process of evaporation
e) Steam rising from a hot girdle when water is sprinkled on it -
Due to heat in the hot girdle, the water sprinkled on the girdle gets converted into water vapours and evaporates.

Note: Remember that when the temperature is high, the process of evaporation will take place whereas, at low temperatures, the process of condensation will.
Evaporation generally takes place in low whereas condensation generally takes place in high altitudes