First law of thermodynamics

First law of thermodynamics

First law of thermodynamics is also known as the law of conservation of energy which may be stated as follows:

"Energy may be converted from one form to another, but cannot be created or be destroyed".

There are many ways of enunciating the first law of thermodynamics. Some of the selected statements are given below:

1.     "Energy of an isolated system must remain constant although it may be changed from one form to another".

2.     "The change in the internal energy of a closed system is equal to the energy that passes through its boundary as heat or work".

3.     "Heat and work are equivalent ways of changing a system's internal energy".

4.     "Whenever other forms of energies are converted into heat or vice versa there is a fixed ratio between the quantities of energy and heat thus converted".

Significance of first law of thermodynamics is that, the law ascertains an exact relation between heat and work. It establishes that ascertain quantity of heat will produce a definite amount of work or vice versa. Also, when a system apparently shows no mechanical energy but still capable of doing work, it is said to possess internal energy or intrinsic energy.