Use the standard molar entropies in Appendix B in the textbook to calculate S at

Question

Use the standard molar entropies in Appendix B in the textbook to calculate S at 25 C for each of the following reactions. Account for the sign of the entropy change in each case.

Part A

2NaHCO3(s)Na2CO3(s)+CO2(g)+H2O(g)

Express your answer as an integer and include the appropriate units.

Part B

2SO2(g)+O2(g)2SO3(g)

Express your answer using one decimal place and include the appropriate units.

Part C

2HgO(s)2Hg(l)+O2(g)

Express your answer using one decimal place and include the appropriate units.

Explanation / Answer

Part A : dSo = dSo(products) - dSo(reactants)

= (138.8 + 213.7 + 188.8) - (2 x 101.7)

= 337.9 J/K.mol

dS is +ve, so entropy has increased

Part B : dSo = dSo(products) - dSo(reactants)

= (2 x 256.8) - (2 x 248.2 + 1 x 205.1)

= - 187.9 J/K.mol

dS is -ve, so entropy has decreased

Part C : dSo = dSo(products) - dSo(reactants)

= (2 x 76 + 1 x 205.1) - (2 x 70.3)

= 216.5 J/K.mol

dS is +ve, so entropy has increased

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