Question

one mole of an ideal gas expands isothermally to five terms its initial volume.calculate the entropy change in terms of r, gas constant

Answer 1

isothermal process
means T =constant

from 1st of thermodynamics ,
dQ = dW =PdV = nRT/V dV
put this in below ,
entropy = dQ/T
=nR dV/V

integrate ,

now,
entropy = nR lnVf/Vi
given ,
n =1
Vf /Vi = 5

now,

entropy = R ln5