Question

Calculate the entropy change for the reaction: 2H2(g) + O2(g) → 2H2O(g)given that the standard molar entropies of H2(g), O2(g), and H2O(g) are 130.7 J/mol.K, 205.0 J/mol.K, and 188.8 J/mol.K, respectively.

Answer 1

To calculate the entropy change  S  for the reaction, we can use the following equation:S = nS products  - nS reactants where n is the stoichiometric coefficient and S is the standard molar entropy of each species.For the given reaction:2H2 g  + O2 g   2H2O g S = [2  S H2O g  ] - [2  S H2 g   + 1  S O2 g  ]Now, we can plug in the given standard molar entropies:S = [2  188.8 J/mol.K] - [2  130.7 J/mol.K + 1  205.0 J/mol.K]S = [377.6 J/mol.K] - [261.4 J/mol.K + 205.0 J/mol.K]S = 377.6 J/mol.K - 466.4 J/mol.KS = -88.8 J/mol.KThe entropy change for the reaction is -88.8 J/mol.K.