Question

In the melting of ice, which one of the conditions will be more favourable?
(A) high temperature and high pressure
(B) low temperature and low pressure
(C) low temperature and high pressure
(D) high temperature and low pressure

Answer 1

Hint: Ice is a crystalline solid which has an ordered structure. Ice is less dense than water therefore it floats in water. The melting of ice is an endothermic process. So, if we supply heat to ice, then more of the ice will melt into liquid water.

Complete step by step solution:
For solving this question, we first need to understand the structure of ice. Ice is a crystalline solid which has an ordered structure. Ice is less dense than water therefore it floats in water. This is because of the intermolecular hydrogen bonding existing between the water molecules due to which they do not undergo packing more compactly.
Now let us look into some of the gas laws that we will be using in order to solve this question.
Boyle’s law: It states that the volume of a given mass of a gas is inversely proportional to its pressure provided that the temperature remains constant.
Also, the melting of ice is an endothermic process. So, if we supply heat to ice, then more of the ice will melt into liquid water.
Now, the melting of ice is an endothermic process which is also accompanied by a change in volume since the volume of ice is more than that of liquid water. Hence both temperature and pressure affect the melting of ice.
At the melting point, both the solid phase and the liquid phase are at equilibrium with each other. The melting point of a solid is defined as the temperature at which the vapour pressure of the liquid phase and the solid phase is at equilibrium (and equal). If we increase the temperature then more solid will melt but the temperature of the system will remain the same as that of the melting point until all of the solid melts.
Since the temperature will remain constant during the melting of ice, hence the volume and pressure will be inversely proportional to each other. Since the melting of ice is accompanied by a decrease in volume, the pressure will increase. Therefore, if we increase the pressure, more ice will melt.

Hence the correct answer is (A) high temperature and high pressure.

Note: Sometimes the melting point and the freezing point for a substance have the same value but they could also be different for other substances. If the temperature of a solid is increased above its melting point then the solid will melt but if we decrease the temperature of a liquid below the melting point then the liquid could freeze or it may still exist as a liquid. If the liquid still exists in the liquid phase below its melting point then it is called supercooling and if we disturb it by shaking it or by any other method then the liquid will freeze. Hence the freezing point for a liquid could be lower than its melting point.