Question

Calculate the standard entropy change for the following reaction at 298 K:CH4(g) + 2O2(g) -> CO2(g) + 2H2O(l) Given the standard entropies of CH4(g), O2(g), CO2(g), and H2O(l) are 186.26 J/K/mol, 205.03 J/K/mol, 213.74 J/K/mol, and 69.95 J/K/mol respectively.

Answer 1

To calculate the standard entropy change  S  for the reaction, we can use the following formula:S = nS products  - nS reactants where n is the stoichiometric coefficient and S is the standard entropy of each species.For the given reaction:CH4 g  + 2O2 g  -> CO2 g  + 2H2O l S = [1  S CO2  + 2  S H2O ] - [1  S CH4  + 2  S O2 ]Using the given standard entropies:S = [1  213.74 J/K/mol + 2  69.95 J/K/mol] - [1  186.26 J/K/mol + 2  205.03 J/K/mol]S = [213.74 + 139.9] - [186.26 + 410.06]S = 353.64 - 596.32S = -242.68 J/K/molThe standard entropy change for the reaction at 298 K is -242.68 J/K/mol.