Comment on the following statements:
(a) Rate of evaporation of an aqueous solution decreases with increase in humidity.
(b) Evaporation produces cooling.
(c) Conversion of solid state to liquid state is called fusion. What is meant by latent heat of fusion?
Answers
Answer:
a) If humidity is high, then air is already saturated with water vapours, i.e., it has a lot of water vapours. Therefore, it will not take more water vapours easily. Hence, rate of evaporation decreases.
b) Evaporation produces cooling. This is based on the fact that when a liquid evaporates, it takes (or draws) the latent heat of vaporization from 'another matter' which it touches. This another matter' looses heat and gets cooled. Therefore, evaporation causes cooling.
c) Latent heat of fusion is the heat required to melt the solid state to liquid state without increase in temperature. It is the amount of heat required per unit mass of a substance at melting point (constant) and under 1 Atmosphere pressure to convert it from the solid to the liquid state.
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Answer:
(a) The statement “the rate of evaporation of aqueous solution decreases with the increase in humidity” is true. Humidity is the moisture present in the atmosphere. A dry atmosphere can hold more water molecules compared to a humid atmosphere. Hence, when the humidity increases the rate of evaporation decreases and vice-versa.
(b) Evaporation causes cooling because, in the phase transition of a liquid to vapor, energy is absorbed in the form of heat from the surrounding. Hence, it results in a cooling effect.
(c) The latent heat of fusion or enthalpy of fusion is defined as the amount of heat (in joules) that is required to convert 1 kg of solid to liquid at a constant temperature. This heat provides energy to the solid and triggers it to convert to liquid form.
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