Entropy of Reaction

Question

Use the data from this table, https://sites.google.com/site/chempendix/thermo of thermodynamic properties to calculate the values of ΔS°rxn for each of the following reactions at 25 °C.

a) 2CO(g) + O₂(g) ---> 2CO₂(g)

Change in S^o_rxn= _____ J/K

b) C₃H₈(g) +5O₂(g) -----> 3CO₂(g) +4H₂O(l)

Change in S^o_rxn= _____ J/K

Answer 1

ΔS^o_rxn = S^o_products - S^o_reactants

a. ΔS^o_rxn = 2S^o_CO2 - (2S^o_CO + S^o_O2)

= 2•213.8 - (2•197.7 + 205.2) = -173.0 J/K

b. ΔS^o_rxn = (3S^o_CO2 + 4S^o_H2O) - (S^o_C3H8 + 5S^o_O2)

= (3•213.8 + 4•70.0) - (270.3 + 5•205.2) = -374.9 J/K

The H₂O in b. is (l), everything else in a. and b. is (g)