Question

The melting point of ice
A. Increases with increasing pressure
B. Decreases with increasing pressure
C. Is independent of pressure
D. Is proportional to pressure

Answer 1

Hint: Use the knowledge of the second law of thermodynamics and LeChatelier's principle. Entropy plays an important role in the changes occurring in the system. A system always wants to be in equilibrium.

Complete Step-by-Step solution:
The answer could be explained using LeChatelier's principle which states that when a system is in equilibrium, any external changes that try to take it out of equilibrium (like applying pressure to ice) will cause the system to adjust in a way to counteract that change.
A system wants to be in equilibrium. A state of equilibrium means a system has achieved maximum entropy. This is why when we change external factors such as pressure the system undergoes changes in order to maintain its equilibrium and this is the reason the transition temperature of the system changes with external factors such as pressure. For most of the systems, the melting point increases with an increase in pressure except for water. This strange behavior of the water ice system is observed because water expands when it freezes i.e. ice occupies more volume than liquid water. So when the external pressure is increased the ice water system maintains its entropy by occupying a smaller volume and since water occupies less volume, more and more ice is converted into water resulting in a decrease in melting point.
Correct Option is B. Decreases with increase in pressure.

Note: Remember that transition temperature depends on the external changes of the system. Ice is an exceptional case in which the melting point decreases with an increase in pressure. This happens because the system wants to be in equilibrium.