Consider an ideal gas confined in a cylinder with a frictionless piston. The reversible

expansion of gas takes place in a finite number of infinitesimally small

intermediate steps. If the P

pressure of gas ‘P’ by ‘dP’. Then gas expands reversibly and piston moves

through a distance ‘dl’.

expansion of gas takes place in a finite number of infinitesimally small

intermediate steps. If the P

_{ext}is infinitesimally less than internalpressure of gas ‘P’ by ‘dP’. Then gas expands reversibly and piston moves

through a distance ‘dl’.

Since dP is so small, for all practical purposes.

P

_{ext.}– P_{gas}= P.One work done by gas in one infinitesimal step (dw) can be expressed as;

dw = P ´ dV. [ w = P ´ DV]

\dw = PdV.

If the gas expands from V

reversible expansion. The total amount of work done would be equal to

_{1}to V_{2 }during isothermalreversible expansion. The total amount of work done would be equal to

What if the number of moles is not constant..?

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