Question

What is pressure-volume work? Distinguish between isothermal process and adiabatic process.

Answer 1

Pressure -Volume work done occurs when the volume of the gas or system changes. Work done by a system is the energy transferred from it to its surroundings. Express that work in joules and calories, $-{{\text{P}}_{\text{external}}}\times \text{ }\vartriangle \text{V}$. Isothermal means constant temperature and adiabatic means no heat exchange.

Complete step by step answer:
The work done by the gas is specifically the expansion and compression of the gas. Work done by gases is sometimes called pressure-volume or PV work. To calculate how much work is done (or has done to it) by the gas against a constant external pressure, the formula of work done is:
WORK= (w) = $-{{\text{P}}_{\text{external}}}\times \vartriangle \text{V}$ : where external pressure is denoted by ${{\text{P}}_{\text{external}}}$. The external pressure opposes the pressure of the gas in the system. ${\vartriangle \text{V}}$ is the change in the volume of the gas, which is calculated as ${{\text{V}}_{\text{final}}}-{{\text{V}}_{\text{initial}}}$.
- Sign convention of work are:
When the gas does work, the volume of the gas particles decreases ($\vartriangle \text{V}$<0).The work done is positive.
When the gas does work, the volume of the gas particles increases ($\vartriangle \text{V}$>0).The work done is negative.

The differences between isothermal process and adiabatic process are:

ISOTHERMAL PROCESS	ADIABATIC PROCESS
It is a thermodynamic process in which temperature remains the same.	It is a thermodynamic process in which there is no heat exchange between system and its surrounding.
Transference of heat occurs.	There is no heat transfer.
Temperature is constant during the process.	Temperature change may or may not occur.
Work done is due to the change in the net heat content of the system.	Work done is due to the change in its internal energy.

Note: The slope of reversible adiabatic process is very steep than reversible isothermal process when pressure is plotted against volume of a gas. So, the work done in a reversible isothermal process is more than a reversible adiabatic process taking initial and final positions to be the same in both processes. As, work done is area under P-V graph.