What is the value for ∆Soreaction for the following reaction, given the standard entropy values? Fe2O3 (s) + 3H2 (g) 2 Fe (s) + 3H2O (g) + 138 J/K - 138 J/K + 5 J/K - 5 J/K 189 J/K

Answer: 138 J/K

Explanation:

1) ΔS reaction = ΔS products - ΔS reactants

2) ΔS products = 2ΔS Fe (s) + 3 ΔS H₂O (g)

3) ΔS reactants = ΔS Fe₂O₃ (s) + 3 ΔS H₂ (g)

4) Now you have to search the standard entropy values for each product and each reactant in a table.

I found these values at 25° and 1 bar.

ΔS H₂O = 188.8 J/Kₓmol

ΔS Fe (s) = 27.3 J/Kmol

ΔS Fe₂O₃ (s) = 87.4 J/Kmol

ΔS H₂ (g) = 130.7 J/Kmol

5) Replace those values into above equations:

ΔS products = 2ΔS Fe (s) + 3ΔS H₂O (g) =

2 mol * 27.3 J/K*mol + 3 mol * 188.8 J/K*mol = 621.0 J/K

ΔS reactants = ΔS Fe₂O₃ (s) + 3 ΔS H₂ (g) =

1mol * 87.4 J/K*mol + 3*130.7 J/K*mol = 479.5 J/K

ΔS reaction = 621.0 J/K - 479.5 J/K = 141.5 J/K

Taking into account the differences in the values from different sources (specially due to the temperature), you can consider that the value 141.5 J/K is pretty much close to 138 J/K, and take that answer.