Question

What is the change in entropy (ΔS) when 1 mole of hydrogen gas (H2) reacts with 1 mole of chlorine gas (Cl2) to form 2 moles of hydrogen chloride gas (2HCl) at a temperature of 298 K and a pressure of 1 atm?

Answer 1

To calculate the change in entropy  S  for the reaction, we need to find the difference between the entropy of the products and the entropy of the reactants. We can use the standard molar entropies  S  for each substance at 298 K and 1 atm, which can be found in standard thermodynamic tables.Standard molar entropies  S  at 298 K and 1 atm:H2 g  = 130.68 J/molKCl2 g  = 223.07 J/molKHCl g  = 186.90 J/molKThe balanced chemical equation for the reaction is:H2 g  + Cl2 g   2HCl g Now, we can calculate the change in entropy  S  using the following equation:S = S products  - S reactants S = [2 * S HCl ] - [S H2  + S Cl2 ]S = [2 * 186.90 J/molK] - [130.68 J/molK + 223.07 J/molK]S = [373.80 J/molK] - [353.75 J/molK]S = 20.05 J/molKThe change in entropy  S  for the reaction is 20.05 J/molK.