Chapter 9, Problem 18QAP

Consider the phase diagram of the compound in Problem 17 to answer the following questions.

(a) What is the physical state of the compound at 35 mm Hg and 120°C?

(b) What is the normal freezing point of the compound?

(c) What is the point A called?

(d) What is the point B called?

(e) What is the point C called?

(f) What change occurs when at a constant pressure of 33 mm Hg, the temperature is decreased from 40°C to -20°C?

(g) Will the solid float on the liquid?

(h) Can the compound exist as a liquid at 180°C and 2 atm pressure?

Interpretation Introduction

(a)

Interpretation:

Refer to the given phase diagram of compound X. The physical state of compound X is to be determined at pressure 35mmHg and temperature 120°C.

Concept introduction:

Phase diagram can be defined as the representation of pressure and temperature quantities of any pure substance. At these values of temperature and pressure, the different phases of the pure substance are equilibrium to each other.

Answer to Problem 18QAP

The physical state of compound X is vapor determined at pressure 35mmHg and temperature 120°C.

Explanation of Solution

Given Infromation:

The phase diagram of the compound X is as follows:

The triple point is defined as the equilibrium condition among all the three phases of any pure substance which is solid, liquid and gas. The curves are used for the equilibrium condition between two phases of pure substance. The phase diagram is shown below-

In the below diagram −

a = solid-liquid phase in equilibrium

b = liquid-vapor phase in equilibrium

c = solid-vapor phase in equilibrium

Given values-

Pressure = 35mmHg

Temperature = -50°C

These two given values are intersecting at point D and point D lies in the vapor phase region.

Hence,

At pressure 35 mmHg and at temperature 120°C, the physical state of the compound is vapor.

Interpretation Introduction

(b)

Interpretation:

The normal freezing point of a compound is to be determined.

Concept introduction:

Phase diagram can be defined as the representation of pressure and temperature quantities of any pure substance. At these values of temperature and pressure, the different phases of the pure substance are equilibrium to each other.

Answer to Problem 18QAP

The normal freezing point of a compound is 20°C.

Explanation of Solution

The triple point is defined as the equilibrium condition among all the three phases of any pure substance which is solid, liquid and gas. The curves are used for the equilibrium condition between two phases of pure substance. The phase diagram is shown below-

In the above diagram −

a = solid-liquid phase in equilibrium

b = liquid-vapor phase in equilibrium

c = solid-vapor phase in equilibrium

The normal boiling temperature is the temperature at which compound start freezing which is basically atmospheric pressure. Therefore pressure for the freezing point is 760mmHg. At atmospheric pressure of freezing point, if at the particular temperature the liquid and vapor phase of a substance are at equilibrium then that temperature is the freezing point temperature. From the phase diagram of the compound, at temperature 20°C liquid and vapor phase of a substance is at the equilibrium.

Hence, the freezing point temperature is 20°C.

Interpretation Introduction

(c)

Interpretation:

The name for the point A is to be determined.

Concept introduction:

Phase diagram can be defined as the representation of pressure and temperature quantities of any pure substance. At these values of temperature and pressure, the different phases of the pure substance are equilibrium to each other.

Answer to Problem 18QAP

The A is the critical point of the phase diagram of the compound.

Explanation of Solution

The triple point is defined as the equilibrium condition among all the three phases of any pure substance which is solid, liquid and gas. The curves are used for the equilibrium condition between two phases of water. The phase diagram is shown below-

In the above diagram −

a = solid-liquid phase in equilibrium

b = liquid-vapor phase in equilibrium

c = solid-vapor phase in equilibrium

From the above diagram, the critical point of a substance is represented by the end of that curve which shows the equilibrium condition between the liquid phase and vapor phase. This curve is curved b and it ends at point A at temperature 200°C and at pressure 2 atm.

Hence, the point A is called a critical point.

Interpretation Introduction

(d)

Interpretation:

The name for the point B is to be determined.

Concept introduction:

Phase diagram can be defined as the representation of pressure and temperature quantities of any pure substance. At these values of temperature and pressure, the different phases of the pure substance are equilibrium to each other.

Answer to Problem 18QAP

The point B is the triple point in the phase diagram.

Explanation of Solution

The triple point is defined as the equilibrium condition among all the three phases of any pure substance which is solid, liquid and gas. The curves are used for the equilibrium condition between two phases of water. The phase diagram is shown below-

In the above diagram −

a = solid-liquid phase in equilibrium

b = liquid-vapor phase in equilibrium

c = solid-vapor phase in equilibrium

The triple point represents the equilibrium among all the phases which are solid, liquid and gas of compound. Hence, the intersection point of all curves am and c will represent the triple point. From the graph, the intersection point of these three curves is existing at point B.

Therefore, point B will represent the triple point of the compound.

Interpretation Introduction

(e)

Interpretation:

The name for the point C is to be determined.

Concept introduction:

Phase diagram can be defined as the representation of pressure and temperature quantities of any pure substance. At these values of temperature and pressure, the different phases of the pure substance are equilibrium to each other.

Answer to Problem 18QAP

The point C is the normal boiling point for the compound.

Explanation of Solution

The triple point is defined as the equilibrium condition among all the three phases of any pure substance which is solid, liquid and gas. The curves are used for the equilibrium condition between two phases of water. The phase diagram is shown below-

In the above diagram −

a = solid-liquid phase in equilibrium

b = liquid-vapor phase in equilibrium

c = solid-vapor phase in equilibrium

The point C is the normal boiling point at which the compound starts boiling and the pressure for this is atmospheric pressure or 1 atm or 760 mmHg.

Interpretation Introduction

(f)

Interpretation:

The changes are to be determined at constant pressure 33mmHg and the temperature is changing from 40°C to -20°C.

Concept introduction:

Phase diagram can be defined as the representation of pressure and temperature quantities of any pure substance. At these values of temperature and pressure, the different phases of the pure substance are equilibrium to each other.

Answer to Problem 18QAP

At constant pressure 33mmHg and the process of changing of temperature from 40°C to -20°C is occurred between point E and F. In this process-

There is a change of phase.

Explanation of Solution

The triple point is defined as the equilibrium condition among all the three phases of any pure substance which is solid, liquid and gas. The curves are used for the equilibrium condition between two phases of water. The phase diagram is shown below-

In the above diagram −

a = solid-liquid phase in equilibrium

b = liquid-vapor phase in equilibrium

c = solid-vapor phase in equilibrium

In this process the, the pressure is constant and the temperature varies from 40°C to -20°C which is represented by point E and F. The starting point is E and endpoint is F and both have different phases. The point E or starting point occurs in the vapor phase and the ending point, point F lies in the solid phase. So, there is an occurrence of a change of phase.

Interpretation Introduction

(g)

Interpretation:

The statement that solid float on liquid is to be checked.

Concept introduction:

Phase diagram can be defined as the representation of pressure and temperature quantities of any pure substance. At these values of temperature and pressure, the different phases of the pure substance are equilibrium to each other.

Answer to Problem 18QAP

The densest phase is a solid phase.

Explanation of Solution

The triple point is defined as the equilibrium condition among all the three phases of any pure substance which is solid, liquid and gas. The curves are used for the equilibrium condition between two phases of water. The phase diagram is shown below-

In the above diagram −

a = solid-liquid phase in equilibrium

b = liquid-vapor phase in equilibrium

c = solid-vapor phase in equilibrium

The floating of solid on liquid depends on the density of these two phases. In the case of the solid phase of water, it will float on the liquid phase of water. But this condition is not the same in all condition because the solid iron piece will not be able to float on the liquid water otherwise it will sink in the water.

Interpretation Introduction

(h)

Interpretation:

The existence of compound at pressure 2 atm and at temperature 180°C is to be determined.

Concept introduction:

Phase diagram can be defined as the representation of pressure and temperature quantities of any pure substance. At these values of temperature and pressure, the different phases of the pure substance are equilibrium to each other.

Answer to Problem 18QAP

The compound at pressure 2 atm and at temperature 180°C will exist as a liquid.

Explanation of Solution

The triple point is defined as the equilibrium condition among all the three phases of any pure substance which is solid, liquid and gas. The curves are used for the equilibrium condition between two phases of water. The phase diagram is shown below-

In the above diagram −

a = solid-liquid phase in equilibrium

b = liquid-vapor phase in equilibrium

c = solid-vapor phase in equilibrium

The compound with pressure 2 atm and at temperature 180°C is occurred at point G which exist at the left of the critical point or point A. The pressure of this pint is less than the critical point hence it will exist in the critical limits. Therefore, the phase of the compound at this point is the liquid phase. Therefore, compound will exist as a liquid at given quantities.