First Law of Thermodynamics:
The first law of thermodynamics is nothing, but energy conservation applied to a thermodynamic system. When a system takes some amount of heat from its surroundings. It is used up in two ways:
1. A part of it increases the internal energy of the system
2. The remaining part is converted into some external work done by the system.
So,
Heat absorbed = Rise in internal energy + external work done.
This is the first law of thermodynamics is, in essence, the energy conservation law which is applicable to every thermodynamic system together with its surroundings.
Second Law of Thermodynamics:
The first law of thermodynamics can’t determine this natural direction. So, it is important to formulate a new law – the second law of thermodynamics.
Scientists expressed the second law in different forms. However, all of the different forms are equivalent. They provide an alternative statement of the same physical law.
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1. Clausius Statement: No self-acting machine can transfer heat from a lower to a higher temperature.
2. Kelvin-Planck Statement: No self-acting machine can convert some amount of heat entirely into work.