in the concept of latent heat applicable during transformation of gaseous Phase to liquid phase and from liquid phase to solid phase
Answers
The intermolecular forces of attraction amongst liquids are weaker than those amongst solids hence liquids do not have a definite shape but the forces are strong enough so that liquids have a definite volume. Liquids display properties like viscosity, flow, etc. They are comparatively more compressible as compared to solids.
To convert liquids into gas you need to heat the liquid beyond its boiling point. This process is the process of ‘Boiling’ or ‘vaporization’. Hence, to convert a liquid to a solid we cool it below its freezing point. This process is known as ‘Freezing’. During vaporization or freezing, the constituents of the liquid are in thermal equilibrium with the constituents of the other states (gas or liquid).
Gas
solid liquid gas
The molecules of a substance in this state have the least intermolecular forces of attraction amongst them. Gases display properties like dispersion and compression. To convert gases to liquids we cool them below their boiling point. This process is the process of ‘Condensation’.
When a change in state is going on, the thermal dynamics of the system get very interesting. For example, if you keep heating a substance, it changes its state with the absorption of temperature. But the absorption of temperature is not uniform. Let us see how it happens!
Latent Heat
When the change of state is studied carefully, we see that the temperature of a substance remains constant during a change in the state! This is very strange. As if the change in state opens up new portals or spaces where our supplied energy hides. Therefore we call this hidden energy, the latent or the hidden heat. Let us understand this with an example:
solid liquid gas
Suppose we have a block of ice we want to convert to water. We all know that ice turns to water and vice versa at 0°C. Now assume we start heating ice at 0°C. You will observe that when we do so, the temperature of ice does not change. It starts converting to water but the temperature does not rise until the entire ice block has been converted to water. But we are heating the ice block right? So, what happened.
If a mass ‘m’ of any substance undergoes a change in state by absorbing an amount of heat, Q at a constant Temperature T, then we have:
L = Q/m or Q = mL
All the heat supplied to the ice at 0 0C is used by the ice to change its phase from solid to liquid. Thus the heat supplied is not used up to raise the temperature of the substance. There are 2 kinds of Latent heat:
Latent Heat of Fusion
The heat energy supplied per unit mass of a substance at its melting point to convert the state of the substance from solid to liquid is known as Latent heat of Fusion. Latent heat of Fusion of water is 334 Joules/gram of water.
Latent Heat of Vaporization
The heat that a substance absorbs per unit mass at its boiling point to convert the phase of the substance from liquid to gas is the Latent heat of Vaporization. Latent heat of Vaporization of water is 2230 Joules/gram of water.
Now similarly, if you want to convert the phase of a substance from a gas to liquid or from liquid to solid you need to cool the substance to its boiling point or melting point as the conditions demand and then extract the amount of Latent heat to facilitate the phase change.