Question

When pressure is applied to the equilibrium system: $ice \rightleftharpoons water$ , which of the following phenomena will happen?
Options-
a.More ice will be formed
b.Ice will sublime
c.More water will be formed
d.Equilibrium will not be disturbed.

Answer 1

The equilibrium between ice and water is called a one component phase equilibrium as it involves the solid and liquid phase of a single chemical entity. The equilibriums are sensitive to changes in physical conditions like temperature, pressure or volume.

Complete answer:
The process of transformation of water into ice is called freezing and the reverse process is known as melting. At the standard conditions of pressure, the solid and liquid equilibrium for water exists at $273K$ .
Water is a single chemical entity that changes its phases with the changing physical conditions and therefore it is called a one component system. Since two phases are in an equilibrium, the values of phases and components can be put into the phase rule equation to know the degrees of freedom.
The phase rule can be written as follows:
$F = C - P + 2$
With one component and two phases in the equilibrium $ice \rightleftharpoons water$
$F = 1 - 2 + 2 = 1$
With only one degree of freedom, the change in pressure brings a change in temperature as well.
According to Le Chatelier’s principle, an increase in pressure will be compensated by shifting the reaction in the forward direction so as to decrease volume. Water occupies less volume as compared to ice and therefore the equilibrium promotes the formation of water.
The increasing pressure also decreases the melting point of the system, therefore with an increased pressure, the ice present in equilibrium is at a temperature higher than the melting point and it starts melting to give more water so as to maintain the equilibrium.

$\Rightarrow$ Thus, we get more water on applying pressure to the equilibrium of $ice \rightleftharpoons water$ and option (c) is correct.

Note:
Degree of freedom in a phase equilibrium is used to define the number of parameters or physical conditions that must be specified so as to completely know the state of a system. With a single degree of freedom, any change in one of the variables brings a corresponding change in another variable.