The volume of 0.100 mol of helium gas at 34°C is increased isothermally from 1.00 L to 4.50 L. Assuming the gas to be ideal, calculate the entropy change for the process.

Answer 1

It would appear from the site below that delta S = ln(v2/v1) since T is constant.
http://web.mit.edu/16.unified/www/SPRING/propulsion/notes/node39.html