Question

In this phase diagram for water, indicate the direction that the solid-liquid and liquid-gas coexistence lines will move after the addition of solute.

In this phase diagram for water, indicate the direction that the solid-liquid and liquid-gas coexistence lines will move after the addition of solute.

Answer 1

Concepts and reason

The concept used to solve this problem is the phase diagram of water.

In the phase diagram of water, the solid-liquid coexistence line will move towards left after the addition of solute because of depression in freezing point of water upon the addition of solute.

The liquid-gas coexistence line will move towards right after the addition of solute because of elevation in boiling point of water upon the addition of solute.

Fundamentals

A phase diagram is a graph of pressure versus temperature depicting the solid, liquid and gaseous phases of a single substance under different conditions of temperature and pressure.

In the phase diagram of water, the solid-liquid coexistence line indicates the point at which the solid converts to liquid.

The temperature corresponding to $P = 1{\rm{ atm}}$ at the solid-liquid coexistence line in the phase diagram of the water is the freezing point of water.

When solute is added to the water, there is a lowering in the vapour pressure of the solution. Consequently, there is a lowering of freezing point of the water.

So, the direction of solid-liquid coexistence line will be towards the left, that is towards lower temperatures, after the addition of solute.

In the phase diagram of water, the liquid-gas coexistence line indicates the point at which the liquid converts to gas.

The temperature corresponding to $P = 1{\rm{ atm}}$ at the liquid-gas coexistence line in the phase diagram of the water is the boiling point of water.

When solute is added to the water, there is a lowering in the vapour pressure of the solution. Consequently, there is an elevation of boiling point of the water.

So, the direction of liquid-gas coexistence line will be towards the right, that is towards higher temperatures, after the addition of solute.

Ans:

The direction of solid-liquid and liquid-gas coexistence lines after the addition of solute is: