JEE Main & Advanced Physics Thermodynamical Processes First Law of Thermodynamics (FLOT)

(1) It is a statement of conservation of energy in thermodynamical process.

(2) According to it heat given to a system \[(\Delta Q)\] is equal to the sum of increase in its internal energy \[(\Delta U)\] and the work done \[(\Delta W)\] by the system against the surroundings.

\[\Delta Q=\,\Delta U+\Delta W\]

(3) It makes no distinction between work and heat as according to it the internal energy (and hence temperature) of a system may be increased either by adding heat to it or doing work on it or both.

(4) \[\Delta Q\] and \[\Delta W\] are the path functions but \[\Delta U\] is the point function.

(5) In the above equation all three quantities \[\Delta Q,\,\Delta U\]and \[\Delta W\] must be expressed either in Joule or in calorie.

(6) The first law introduces the concept of internal energy.

(7) Limitation : First law of thermodynamics does not indicate the direction of heat transfer. It does not tell anything about the conditions, under which heat can be transformed into work and also it does not indicate as to why the whole of heat energy cannot be converted into mechanical work continuously.   Useful sign convention in thermodynamics