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First law of Thermodynamics

Energy can neither be created nor be destroyed, although it can be converted from one form to another.

Justification of First Law of Thermodynamics

If a closed system having E1 internal energy supplies “q” amount of heat, then the internal energy of the system becomes (E1 + q).
If work (w) is done on the system, then its internal energy further increases and becomes E2. Thus,
E2 = E1 + q + w
or ΔE = q + w
In case q is the heat absorbed and w is the work done by the system, then
ΔE = q + (–w) = qw
Thus, the first law of thermodynamics may also be stated as “the net energy change of a closed system is equal to the heat absorbed plus the work done on the system or minus the work done by the system.

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