How do you calculate entropy change?
This example problem demonstrates how to calculate the change in entropy of a system's and surroundings following a chemical reaction at constant temperature and pressure.
Calculate the entropy of the surroundings for the following reaction.
a.) C2H8(g) + 5 O2(g) → 3 CO2(g) + 4H2O(g)
ΔH = -2045 kJ, the reaction takes place at 2
This reaction is an exothermic reaction. The negative sign of enthalpy change ( -2045 kJ) shows that the system has lost 2045 kJ of energy to surroundings.
ΔSsurr = ΔH /T = + 2045 kJ ( heat gained by surroundings) / 298.15 K
ΔSsurr = 6.86 kJ / K
Good example with generic equation here: http://chemwiki.ucdavis.edu/Physical_Chemistry/Thermodynamics/State_Functions/Entropy/Calculating_Entropy_Changes