Properties of Pure Substance

Pure Substance:

A substance that has fixed chemical compositions throughout is called a pure substance. Phases of pure substances are:

• Solid
• Liquid
• Gas

States during a Phase Change Process:

There are different phases of matter during a Phase Change Process and they are:

• (1) ↝ Compressed Liquid 
• (2) ↝ Saturated Liquid 
• (3) ↝ Saturated Liquid-Vapour mixture 
• (4) ↝ Saturated Vapour
• (5) ↝ Superheated Vapour 

Now, we will through light on the above mentioned topics.

1. Compressed Liquid:

The state of liquid during a Phase Change Process which is NOT about to vaporize.

2. Saturated Liquid:

The state of liquid durine a Phase Change Process which is about to vaporize.

3. Saturated Liquid-Vapour Mixture:

The state at which both liquid and Vapour co-exist.

4. Saturated Vapour:

The state of Vapour during a Phase Change Process whicheck is about to condense.

5. Superheated Vapour:

The state of Vapour during a Phase Change Process which is NOT about to condense.

Some related topics are:

a) Saturation Temperatures:

At a given pressure, the temperature at which a pure substance changes phase is called Saturation Temperature.

b) Saturation Pressure:

At a given temperature, the pressure at which a pure substance changes phase is called Saturation Pressure.

c) Critical Pressure:

Pressure of a gas or Vapour at critical point is called Critical Pressure.

At critical point, saturated vapour and liquid states are identical and after that there is no distinct phase process.

Vaccum Cooling:

When the atmospheric pressure over a liquid is reduced, the Vapour pressure needed to induce boiling is also reduced and the boiling point of the liquid decreases. By reducing pressure we can even boil off water at lower temperatures. This rapid evaporation of moisture from the surface and within the products due to the low surrounding pressure, absorbs the necessary latent heat for phase change. This absorption of liquid Vapour from substance produce cooling effect called Vaccum Cooling.

Derivation of Properties of Saturated Mixture:

The derivation of Specific Volume of Saturated Mixture is given in the video below:

Similarly, the equation of enthalpy and internal energy of Saturated Mixture is given by:

Equation of the State:

Any equation that relates pressure, temperature and specific volume oF the sinstance is called EqYatton of the State which is also called Ideal Gas Equation.

Where;

P = Pressure in KPa 

V = Specific Volume in m3/Kg

T = Temperature

R= Gas constant in KJ/Kg.K 

Gas constant ( R ) is different for each gas and is determined by:

Gas Constant = Universal gas constant / Molecular Mass

Compressibility Factor:

Compressibility Factor is the measure of deviation of real gas from ideal gas behaviour.

 Z is the compressibility factor and it's value is 1 for ideal gas.

Reduced Temperature, Pressure and Volume:

Gases behave differently at a given temperature and presure but they behave very much the same at same temperature and pressure normalized with respect to their critical temperatures and pressures.

Here; 

Pr = Reduced pressure 

Tr = Reduced temperature 

Vr = Reduced Specific Volume 

Principle of Corresponding State:

It states that;

The compressibilityfactor for all gases is approximatelythe same at the same reduced temperature and presure.

Other Equations of State:

1. Vander Waal Equation of State:

Vander waal equation of state is given by:

2. Beattie-Bridgeman Equation of State:

This equation of state is given by:

3. Benedict-Webb-Rubin Equation of State:

Equation of state is given by:

4. Virial Equation of State:

Equation of state is given by: