Question

3. For water system, the number of phases at the triple point is _____________

a) 0

b) 1

c) 2

d) 3

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Answer 1

Answer:

The number of phases at the triple point for the water system = $3$.

Therefore, option d) $3$ is correct.

Explanation:

To find:

The number of phases at the triple point for the water system =?

Triple point:

• It is the point of the temperature and the pressure at which the three phases i.e., solid, liquid, and gaseous of any substance co-exist in thermodynamic equilibrium.

As we know,

• The triple point is a fixed point. It does not vary with temperature and pressure.
• It is a single component system with zero degrees of freedom.

By using Gibb's phase rule, we can find out the number of phases present at the triple point for the water system.

• F = $C-P+2$

Here, F = The degrees of freedom in $H_{2}O$ = 0

• C = The number of chemical components in the water system = 1
• P = The number of phases present in the water system

Therefore,

• $0 = 1-P +2$
• P = $3$

Hence, there are $3$ phases at the triple point for the water system.

As we can see in the graph also, the number of phases at the triple point for the water system = $3$.