What is the change in entropy of the gas?

[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]

isothermal process

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

 

[PureEnergy]

This problem can be solved using

$$\Delta S = nC_Pln\frac{V_2}{V_1}+nC_Vln\frac{P_2}{P_1}$$

All you need to do now, is to recall the relationship between an ideal gas and the heat capacity. You don't need the temperature to solve this problem.

 

[PureEnergy]

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

 

[kenallen]

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