The laws of thermodynamics are a set of four fundamental physical laws that describe the behaviour of energy, entropy, and temperature in relation to physical system. These laws govern how energy is transferred and transformed. The detail of Law’s of Thermodynamics are described in this article.
| Zeroth Law of Thermodynamics |
The zeroth law of thermodynamics states that, ” If two systems are each in thermal equilibrium with a third system, then the three system will be in equilibrium with each other “.
When System, ‘A’, is in thermal equilibrium with another System, ‘B’, and also separately in thermal equilibrium with a system, ‘C’, then system, ‘B’ and ‘C’, will also be in thermal equilibrium with each other refere Fig. 1.1. This statement defines the Zeroth law of thermodynamics. The law is based on temperature measurement.
In simple term, it can be said, “Systems that are in thermal equilibrium exist at the same temperature”.
Example:
We can observe the Zeroth law in action by taking a very common thermometer having mercury in a tube. As the temperature increases, this mercury expands since the area of the tube is constant. Due to this expansion, the height is increased. Now, the increase in the height of the mercury label shows the changes in temperature and basically helps us to measure it.
| First Law of Thermodynamics |
The first law of thermodynamics states that ” energy can be neither created nor destroyed during a
process; it can only change forms “. The first law of thermodynamics is also known as the conservation of energy principle.
So the first law of thermodynamics can be stated as follows for a process:
If ” Q ” is the amount of heat transferred to the system and ” W ” is the amount of work transferred from the system during the process, the net energy transfer (Q-W) will be stored into the system. The energy stored into the system is neither heat nor work it is known as the internal energy of the system.
∴ Q − W = ∆E Or, Q = W + ∆E
For an isolated system, there is no interaction of the system with the surrounding.
For an isolated system dQ=0
dW=0
hence, dE=0 or, E=constant
Example:
Consider the heating of water in a pan on top of a range. If 15 kJ of heat is transferred to the water from the heating element and 3 kJ of it is lost from the water to the surrounding air, the increase in energy of the water will be equal to the net heat transfer to water, which is 12 kJ.
| Second Law of Thermodynamics |
Detail
| Third Law of Thermodynamics |