entropy

[daisyi]

One mole of an ideal gas in a cylinder fitted with a piston is made to expand slowly (reversible) from an initial volume of 1x10^3 cm3 to a final volume of 2x10^3 cm3. The cylinder is in contact with a heat reservoir so that, throughout the expansion process, the gas is held at a constant temperature. What is the change in entropy of the gas?

[Doc Al]

For an isothermal process, \Delta S = Q/T.

[PureEnergy]

Along with Doc's equation, you'll want to use [itex]\Delta U = Q + W[/tex]

[kenallen]

but for isothermal process change in internal energy(delta U) is equal to 0.