Question

Calculate the entropy change for the following chemical reaction at 25 °C: 2H2(g) + O2(g) → 2H2O(l) Given that the standard molar entropy of H2(g), O2(g), and H2O(l) are 130.68 J/mol·K, 205.03 J/mol·K and 70.01 J/mol·K respectively.

Answer 1

To calculate the entropy change  S  for the reaction, we can use the formula:S = nS products  - nS reactants where n is the stoichiometric coefficient and S is the standard molar entropy of each species.For the reactants:2 moles of H2 g  have an entropy of 2 * 130.68 J/molK = 261.36 J/molK1 mole of O2 g  has an entropy of 1 * 205.03 J/molK = 205.03 J/molKFor the products:2 moles of H2O l  have an entropy of 2 * 70.01 J/molK = 140.02 J/molKNow, we can calculate the entropy change:S =  140.02 J/molK  -  261.36 J/molK + 205.03 J/molK S = 140.02 J/molK - 466.39 J/molKS = -326.37 J/molKThe entropy change for the reaction is -326.37 J/molK.