Question

At what temperature does delta G become zero for the reaction in Fe2O3 (s) + 3H2-----------2Fe (s) + 3H20 (g)

Answer 1

Let us calculate delta H and delta S first

Fe2O3 (s) + 3H2-----------2Fe (s) + 3H20 (g)

delta H = 2*delta Hf(Fe (s)) + 3* delta Hf(H20(g)) - 3*delta Hf(H2(g)) - delta Hf(Fe2O3(s))
= 2* 0 + 3*(-241.82) - 3*0 - (-824.25)
       = 98.79 KJ/mol
       = 98790 J/mol
         
delta S = 2*delta Sf(Fe (s)) + 3* delta Sf(H20(g)) - 3*delta Sf(H2(g)) - delta Sf(Fe2O3(s))
= 2*27.28 + 3*69.91 - 3*(130.59) - 87.4
       = -214.88 J/mol-K
         
delta G = delta H - T* delta S
0 = 98790 -T*(-214.88)
T = -459.7 K
Answer: -459.7 K

This is not possible to have negative temperature

I think delta Hf values for each element are not correct.

I took them from here:

http://chemistry-reference.com/Standard%20Thermodynamic%20Values.pdf