Laws of thermodynamics - lecture one

Laws of thermodynamics:

laws of thermodynamics

0^th  law: If two bodies A and B are each separately in thermal equilibrium with a third body C, then A and B are also in thermal equilibrium with each other.

1^st law: When a certain amount of heat Q is supplied to a system which does external work W in change of state, the amount of heat is equal to sum of the increase in the internal energy of the system and the external work done by the system. In symbols, the laws expressed as

                   Q = ( U₁  -  U₂ )

2^nd law:

 Lord Kelvin’s statement: “It is impossible to get continuous supply of work from a body by cooling it to a temperature lower than its surroundings.”

Planck’s Statement: “ It is impossible to construct an engine which, working in a complete cycle, will produced no effect other than the rising of a weight and the cooling of a heat reservoir.”

Clausius’s statement: “ It is impossible to for a self acting machine working in cycle process , unaided by external agency, to transfer  heat from a body at a lower temperature to a body at a higher temperature.”

3^rd law: The heat capacities of all solids tend to zero as the absolute zero of temperature is approached and that the internal energies and entropies of all substances become equal there, approaching their common value asymptotically tending to zero.”

Reversible process: A reversible process is one which can be retracted in opposite direction by changing the external conditions infinitesimally. All isothermal and adiabatic operation are reversible when carried out very slowly. There should not be not loss of energy due to conduction, convection or radiation during the cycle of operation.

Irreversible Process: A irreversible process is one which can be retracted in opposite direction by changing the external conditions infinitesimally. In nature all changes are irreversible because of the following reason: 1. The conditions for thermodynamic equilibrium i.e. mechanical, thermal or chemical equilibrium are not satisfied because a natural process does not take place quasi=statically.2. Dissipative effect, such as friction, viscosity, inelasticity, electric resistance, eddy-formation etc. is always present.