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