Question

Which of the following is(are) an endothermic process(es) ?
(i) Dilution of sulphuric acid
(ii) Sublimation of dry ice
(iii) Condensation of water vapours
(iv) Evaporation of water

• A. (i) and (iii)
• B. (ii) only
• C. (iii) only
• D. (ii) and (iv)

Answer 1

Answer: (D)

(ii) and (iv)

Sublimation of ice is a direct phase transition from solid to gas without passing through an intermediate liquid state. The process requires additional energy, therefore, it is an endothermic reaction and the amount of heat absorbed is called heat of sublimation.
$\left[S\right]\stackrel{heat}{\to }\left[V\right]$ ........Sublimation
Evaporation is the process in which water changes from liquid to gas or vapour. This endothermic process occurs with the absorption of heat and the rate of evaporation increases with increase in temperature.
$\left[L\right]\stackrel{heat}{\to }\left[V\right]$ .........Evaporation