Question

State third law of thermodynamics. Give ‘two’ uses.

Answer 1

Hint: The third law of thermodynamics states that the entropy of a perfectly ordered crystalline substance is zero at absolute zero of the temperature.
Complete step-by-step answer:
We have to state the third law of thermodynamics and mention its two uses.
So, let us first discuss the Laws of thermodynamics.
The laws of thermodynamics define the physical quantities, such a temperature, energy, and entropy, that characterize the thermodynamics system at thermodynamic equilibrium.

There are four laws of thermodynamics-

The Zeroth law of thermodynamics-
It states that if two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other.

The first law of thermodynamics-
This law is also known as the Law of Conservation of Energy, and states that energy cannot be created or destroyed in an isolated system.

The second law of thermodynamics-
This law states that the entropy of any isolated system always increases.

The third law of thermodynamics-
This law of thermodynamics states that the entropy of a system approaches a constant value as the temperature of a system approaches a constant value as the temperature approaches absolute zero.
So, we can write that, here S is the entropy of the system and T is the temperature.

Now, the two uses of third law of thermodynamics are-
It is used to determine the absolute entropy of any substance either in solid, liquid or gaseous state at any desired temperature.
It is also used to calculate the thermodynamic properties of a system.

Note – The two very important terms you should be aware of in thermodynamics is “entropy” and “absolute zero”, so entropy is the measure of randomness in a system, it is the core behind the second and third laws of thermodynamics. And absolute zero temperature is the lowest limit of the thermodynamic temperature scale, a state at which the enthalpy and entropy of a cooled ideal gas reach their minimum value, taken as zero kelvins.