[gingi85]

I am having trouble with this problem. I seem to be getting a negative number ...

One mole of a monoatomic ideal gas at T₁=300K and P₁=10atm goes through free expansion at P_ex=2 atm. The W done by the system is 228 calories. What is the change in entropy?

I divided it into two processes: 1) Isobaric from T₁ to T_final, and 2) Isothermic from V₁ to V_final.

V₁ = nRT₁/P₁ = 2.49 m³

P_ex(V₂-V₁)= W

582.7 m³ (!)

T_final = P₂V₂/R = 14042 K (?!?!)

(something tells me I've already made the mistake ...)



Process 1:

delta-S = C_pln(T_final/T₁)

C_p = 3R/2

delta-S = (3*R/2)ln(14042/300) = 47.88 J/K

Process 2:

delta-S = nRln(V_f/V₁) = 8.3ln(582/2.49) = 45.2698 J/K

delta-S_tot = 93.15 J/K

Where did I make the mistake?

[Yggdrasil]

V₁ = 2.49 dm³ since R = 0.08206 dm³ atm mol^-1 K^-1

(1 dm³ = 1 L)