One suggestion for solving fuel-shortage problems is to use electric power (obta

Question

One suggestion for solving fuel-shortage problems is to use electric power (obtained from solar energy) to electrolyze water to form H2(g) and O2(g). The hydrogen could be used as a pollution-free fuel. In the following, enter H and G in kJ and S in J K-1 to two significant figures. Enter the quantities in the order that they appear. (a) Calculate H, S, and G in kJ for burning 1 kg of H2(g) to H2O(l) at 25 o C and 1 atm. (b) Calculate H, S, and G for burning 1 kg of n-octane(g) to H2O(l) and CO2(g) at 25o C and 1 atm.

Explanation / Answer

H2 +1/2O2 = H2O

dH = Hprod - Hreact

dH = (-241.818) + (0 +1/2*0) = -241.818 kJ/mol

dS = Sprod - Sreact

dS = (188.7) - (130.5 + 1/2 * 205) = -44.3 J/K

dG = dH - T*dS = -241.818 *1000 + 298*(-44.3) = -255019.4 J/mol = -255.0 kJ/mol

for

1 kg = 1000 g of H2 --> 1000/2 = 500 mol of H2

dH = 500*-241.818 = -120909 kJ

dS = 500*-44.3 = -22150 J/K

dG = 500*-255019.4 = -127509700 J/mol

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