Question

Calculate the standard entropy change for the reaction of 2 moles of nitrogen gas reacting with 5 moles of oxygen gas to produce 2 moles of nitrogen monoxide gas at a constant pressure of 1 bar and 298 K. Given the standard molar entropy of nitrogen gas, oxygen gas, and nitrogen monoxide gas to be 191.6 J K-1 mol-1, 205.0 J K-1 mol-1, and 210.6 J K-1 mol-1, respectively.

Answer 1

To calculate the standard 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:2 N g  + 5 O g   2 NO g The standard entropy change is:S = [2 moles  210.6 J K-1 mol-1  NO ] - [2 moles  191.6 J K-1 mol-1  N  + 5 moles  205.0 J K-1 mol-1  O ]S = [421.2 J K-1] - [383.2 J K-1  N  + 1025.0 J K-1  O ]S = 421.2 J K-1 - 1408.2 J K-1S = -987.0 J K-1The standard entropy change for the reaction is -987.0 J K-1.