In: Chemistry
What is the entropy change when 1.20 g of propane (C3H8) at 0.100 atm pressure is compressed by a factor of 6 at a constant temperature of 20 ∘C? Assume that propane behaves as an ideal gas
Given, mass of propane = 1.20 g
moles(n) of propane will be = 1.20 g C3H8 x ( 1 mol C3H8 / 44 g C3H8) = 0.027 mol C3H8
P = 0.100 atm
T = 200C = (20+273) K = 293 K
We also know that R = 8.314 J/mol.K
From ideal gas,
PV = nRT
=> PV/nT= R = constant
=> PfVf/nT = PiVi/nT
it is mentioned that Pf =6Pi ( i for initial and f for final)
Now,
PfVf = PiVi
=> Vf /Vi = Pi / Pf
=> Vf /Vi = Pi / 6Pi
=> Vf /Vi = 1/6
Entropy change is given by the relation as:
S = nRln (Vf /Vi)
=> S = 0.027 mol x 8.314 J/mol.K x ln (1/6)
=> S = 0.224478 x ln (0.1667) J/K
=> S = 0.224478 x -1.791559489
=> S = -0.402165691 J/K = - 0.402 J/K
Hence, the answer is - 0.402 J/K .