Question

1. Calculate delta S at 27*c:

2CH4 (g) --> C2H6 (g)+ H2 (g)

2. Calculate delta S at 27*c:

2NH3 (g) --> N2H4 (g) + H2 (g)

3. If delta H (+) and delta S (-) is it spontaneous?

Answer 1

1)
delts Sf (CH4) = 182.26 J/Kmol
delts Sf (C2H6) = 229.60 J/Kmol
delts Sf (H2) =   130.68 J/mol K

delta S(rxn) = delta S (H2) + delta S (C2H6)­ - 2* delta S (CH4)
                         = 130.68 + 229.60 - 2*182.26
                         = -4.24 J/K mol
ANSWER: -4.24 J/K mol

2)
delts Sf (NH3) = 192.45 J/K mol
delts Sf (N2H4) = 121.21 J/K mol
delts Sf(H2) =   130.68 J/mol K

delta S(rxn) = delta S (H2) + delta S (N2H4)­ - 2* delta S (NH3)
                         = 130.68 + 121.21 - 2*192.45
                         = -133.01 J/K mol
Answer: -133.01 J/K mol

3)
for sponataneous, delta G should be negative
delta G = delta H - T* delta S

If delta H (+) and delta S (-) then delta G will be come positive
Hence it is not spontaneous