Heat transfer & work transfer

Heat transfer & work transfer:-
1. Heat transfer and work transfer are the energy interactions. A closed system and its
surroundings can interact in two ways: by heat transfer and by work transfer.
Thermodynamics studies how these interactions bring about property changes in a system.
2.  The same effect in a closed system can be brought about either by heat transfer or by work
transfer. Whether heat transfer or work transfer has taken place depends on what constitutes
the system.
3.  Both heat transfer and work transfer are boundary phenomena. Both are observed at
the boundaries of the system, and both represent energy crossing the boundaries of the system.
4.  It is wrong to say ‘total heat’ or ‘heat content’ of a closed system, because heat or work is not
a property of the system. Heat, like work, cannot be stored by the system. Both heat and
work are the energy is transit.
5.  Heat transfer is the energy interaction due to temperature difference only. All other energy
interactions may be termed as work transfer.
6. Both heat and work are path functions and inexact differentials. The magnitude of
heat transfer or work transfer depends upon the path the system follows during the change of
7.  Heat transfer takes place according to second law of thermodynamics as it tells about the
direction and amount of heat flow that is possible between two reservoirs.

Qualitative difference between heat and work:

Thermodynamic definition of work:- Positive work is done by a system when the sole effect external to the system could be reduced to the rise of a weight.

Thermodynamic definition of heat:- It is the energy in transition between the system and the surroundings by virtue of the difference in temperature.

Sign convention of work and heat:-

 1. Work done by the system is positive
 2. Work done on the system is negative
 3. Heat transfer from the system or heat rejected by the system negative
 4. Heat transfer to the system positive

First law of thermodynamics :- First law of thermodynamics states the general principle of conservation of energy, Energy is neither created nor destroyed, but only gets transformed from one form to another form.

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