Extensive properties The properties of the system, whose value for the entire system is equal to the sum of their values for the individual parts of the system, are called extensive properties.
For example, total volume, total mass and total energy of a system are extensive properties.

Intensive properties The properties of the system, whose value for the entire system is not equal to the sum of their values for the individual parts of the system, are called intensive properties.
For example, temperature, pressure and density of a system are intensive properties.

Second law of thermodynamics: Second law of thermodynamics states that there is a definite limit to the amount of mechanical energy, which can be obtained from a given quantity of heat energy. Second law of thermodynamics defines entropy.

According to Claussius, this lay may be stated as ” It is impossible for a self acting machine working in a cyclic process, to transfer heat from a body at a lower temperature to a body at a higher temperature without the aid of an external agency”.

The second law of thermodynamics has also been stated by Kelvin Planck as ” It is impossible to construct an engine working on a cyclic process, whose sole purpose is to convert heat energy into work.” According to this statement, the second law of thermodynamics is sometimes called as law of degradation of energy.