Question

Consider the reaction C2H5OH(l) ---> C2H6(g) + (1/2)O2(g). Enter ∆S in J K-1 mol1, all others in kJ/mol to two significant figures. (a) Calculate ∆H, ∆S, and ∆G at 25 C and 1 atm. (b) Estimate ∆U at 25 C and 1 atm. (c) Estimate ∆H at 500 C and 1 atm

Answer 1

a)   ∆H = ∆Hproduct - ∆Hreactant

      ∆H = (-86.68 +0) - (-277.7)

     ∆H   = 193 kJ / mol

   ∆G = (-32.89) - (–167.9)

∆G = 135 kJ / mol

T = 25 + 273 = 298 K

∆G = ∆H - T ∆S

135 = 193 - 298 x ∆S

∆S = 0.195 kJ /mol K

∆S = 195 J / k mol

b)

C2H5OH(l) ------------> C2H6(g) + (1/2)O2(g)

change in moles = (1 + 1/2) -0 = 3/2 = 1.5 = n

∆H = ∆U + n R T

193 = ∆U + 1.5 x 8.314 x 10^-3 x 298

∆U = 189.3 kJ /mol