What is the value for

º

for the following reaction, given the standard entropy values?

Al2O3 (s) + 3H2 (g) → 2Al (s) + 3H2O (g)

-35 J/mol·K

+35 J/mol·/K

+179 J/mol·K

-179 J/mol·K

179 J/mol·K entropy value

179 (J/K*mol)

Explanation:

The value for ΔSºreaction for this reaction is calculated as follows:

2 * Sº of Al (s) + 3 * Sº of H2O (g) - 3 * Sº of H2 (g) - S° of Al2O3 (s)

that is, the subtraction of the standard entropy of the reactants to the products.

| Al (s) | H2O (g) | H2 (g) | Al2O3 (s)

standard entropy (J/K*mol) | 28.3 | 188.825 | 130.684 | 50.92

So:

ΔSºreaction = 2*28.3 + 3*188.825 - 3*130.684 - 50.92 ≈ 179 (J/K*mol)