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/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)