Question

First Law of Thermodynamics.

Answer 1

First Law of Thermodynamics

First law of thermodynamics is simply a restatement of principle of conservation of energy. Imagine a gaseous system for which pressure, volume and temperature are related by certain equation of state and is undertaken through a process. If $\Delta Q, \Delta U$ and $\Delta W$ represent the heat given to the system, change in internal energy and work done by the system respectively. During the process the first law of thermodynamic states that

$\Delta Q=\Delta U+\Delta W$

Sign Convention

Heat absorbed by the system is taken as positive while the heat lost by the system is taken as negative.

Work done by the system is taken as positive while work done on a system is taken as negative.

The increase in internal energy of the system is taken as positive while decrease in internal energy is taken as negative.