# NCERT Class 11 Physics Solutions: Chapter 11 – Thermal Properties of Matter-Part 7 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Question 11.16:

Answer the following questions based on the phase diagram of carbon dioxide:

(a) At what temperature and pressure can the solid, liquid and vapor phases of co- exist in equilibrium?

(b) What is the effect of decrease of pressure on the fusion and boiling point of ?

(c) What are the critical temperature and pressure for ? What is their significance?

(d) Is solid, liquid or gas at

Explanation:

The phase diagram for is shown in the following figure. C is the Triple Point of the CO2 Phase Diagram. This Means T …

is the triple point of the phase diagram. This means that at the temperature and pressure corresponding to this point (i.e.. , at ) , the solid, liquid, and vaporous phases of co-exist in equilibrium.

Explanation:

The fusion and boiling points of decrease with a decrease in pressure.

Explanation:

The critical temperature and critical pressure of are respectively. Even if it is compressed to a pressure greater than will not liquefy above the critical temperature.

Explanation:

It can be concluded from the phase diagram of that:

(a) is gaseous at , under pressure

(b) is solid at under pressure

(c) is liquid at under pressure

Question 11.17:

Answer the following questions based on the phase diagram of :

(a) at 1 atm pressure and temperature is compressed isothermally. Does it go through a liquid phase?

(b) What happens when at pressure is cooled from room temperature at constant pressure? (c) Describe qualitatively the changes in a given mass of solid pressure and temperature as it is heated up to room temperature at constant pressure.

(d) is heated to a temperature and compressed isothermally. What changes in its properties do you expect to observe?

No

Explanation:

The phase diagram for is shown in the following figure. C is the Triple Point of the CO2 Phase Diagram. This Means T …

At pressure and at lies to the left of (triple point ) . Hence, it lies in the region of vaporous and solid phases.

Thus, condenses into the solid state directly, without going through the liquid state.

It condenses to solid directly.

Explanation:

At pressure, lies below (triple point ) . Hence, it lies in the region of vaporous and solid phases. Thus, it condenses into the solid state directly, without passing through the liquid state.

The fusion and boiling points are given by the intersection point where this parallel line cuts the fusion and vaporization curves.

Explanation:

When the temperature of a mass of solid (at 10 atm pressure and at ) is increased, it changes to the liquid phase and then to the vaporous phase. It forms a line parallel to the temperature axis at . The fusion and boiling points are given by the intersection point where this parallel line cuts the fusion and vaporization curves.

It departs from ideal gas behaviour as pressure increases.

Explanation:

If is heated to and compressed isothermally, then it will not exhibit any transition to the liquid state. This is because is higher than the critical temperature of . It will remain in the vapour state, but will depart from its ideal behaviour as pressure increases.

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