Thermodynamics

Definition

Thermodynamics is the study of the flow and transformation of energy within physical systems, particularly in processes involving the exchange of heat and work.

Zeroth Law of Thermodynamics - Thermal equilibrium:

If two systems are in thermal equilibrium with a third system, they are in thermal equilibrium with each other.

This law defines temperature as a measurable and transitive property.

T_A ​= T_B ​and T_B ​= T_C ​⟹ T_A ​= T_C​

First Law of Thermodynamics - Energy Conservation:

“Energy cannot be created or destroyed, only converted from one form to another.”

ΔU = Q - W

(ΔU) - change in internal energy of a system

(Q) - heat added to the system

(W) - work done by the system.

If you add heat to a system, it can increase the system's internal energy or be used to do work.

Second Law of Thermodynamics- Entropy:

Heat cannot spontaneously flow from a hotter body to a colder body, unless external work is done.

So where,

ΔW = 0,

∴

ΔU = ΔQ

It also introduces the concept of entropy, indicating that the total entropy of an isolated system can never decrease over time.

Third Law of Thermodynamics - Absolute zero:

It’s impossible to cool a system to absolute zero in a finite number of steps.

As the temperature of a system approaches absolute zero, the entropy of a perfect crystal approaches a constant minimum.