First Law of Thermodynamics - Defination, Equations and Process
Defination:
According to the first law of thermodynamics, the heat supplied to a thermodynamic system is equal to the sum of the change in internal energy of the system and the work done by the system.
Equation :
$\boxed{\Delta Q = \Delta U + \Delta W}$
where,
$(\Delta Q)$ is the heat supplied to the system,
$(\Delta U)$ is the change in internal energy,
$(\Delta W)$ is the work done by the system.
First Law in Different Thermodynamic Processes :
1. Isothermal Process :
For an isothermal process,
$\Delta T = 0$
For an ideal gas,
$\Delta U = 0$
Hence, from the first law,
$\boxed{\Delta Q = \Delta W}$
2. Isochoric Process :
For an isochoric process,
$\Delta V = 0$
Work done,
$\Delta W = P \Delta V = 0$
Therefore,
$\boxed{\Delta Q = \Delta U}$
3. Isobaric Process :
For an isobaric process,
$\Delta P = 0$
Work done,
$\Delta W = P \Delta V$
Hence,
$\boxed{\Delta Q = \Delta U + P\Delta V}$
4. Adiabatic Process
For an adiabatic process,
$\Delta Q = 0$
From the first law,
$\Delta U = -\Delta W$
5. Cyclic Process
In a cyclic process, the system returns to its initial state. Therefore,
$\Delta U = 0$
Hence,
$\boxed{\Delta Q = \Delta W}$
6. Process for an Isolated System
In an isolated system, there is no exchange of heat and no work is done.
$\Delta Q = 0$ and $\Delta W = 0$
From the first law,
$\boxed{\Delta U = 0}$