What is the absolute entropy of 2.5 mol of gaseous methane at 1.3 bar and 298 K?
The JANAF Thermochemical tables give an absolute entropy value of
44.49 cal/mol*degK at 1.0 bar and 298 K. Apply a pressure correction to that. Also multiply by the number of moles, 2.5.
You will find the pressure correction formula you need at
http://en.wikipedia.org/wiki/Entropy