A. ) Standard enthalpies for selected substances at 25C Substance S(J/(molK)) O2

Question

A. ) Standard enthalpies for selected substances at 25C Substance S(J/(molK)) O2(g) 205.2 SO2(g) 248.2 SO3(g) 256.8 H2O(g) 188.8 H2S(g) 205.8

Calculate Srxn for the balanced chemical equation = H2S(g)+2O2(g)H2O(g)+SO3(g) ?? Express the entropy change to four significant figures and include the appropriate units.

B.)

Standard Thermodynamic Quantities for Selected Substances at 25 C

Part B reaction ( H, 187.2 kJ) .= For the reaction in part B calculate Srxn at 25 C.= ?

Part C reaction (H, 182.6 kJ) =For the reaction in part C calculate Srxn at 25 C. ?

Part D reaction (H, -77.6 kJ) =For the reaction in part D calculate Srxn at 25 C. ?

Substance Hf(kJ/mol) S(J/molK) CH4(g) 74.6 186.3 C2H6(g) 84.68 229.2 H2(g) 0 130.7 N2(g) 0 191.6 NH3(g) 45.9 192.8 N2H4(g) 95.4 238.5 NO(g) 91.3 210.8 O2(g) 0 205.2 KCl(s) 436.5 82.6 KClO3(s) 397.7 143.1

Explanation / Answer

For,

H2S(g) + 2O2(g) ----> H2O(g) + SO3(g)

dSorxn = dSo(products) - dSo(reactants)

             = (188.8 + 256.8) - (205.8 + 2 x 205.2)

             = 445.6 - 616.2

             = -170.6 J/K-mol

dGorxn = (-228.59 - 371.08) - (-33.05) = -566.62 kJ

Part B ) with, dH = 187.2 kJ

dSorxn = (187.2 + 566.62)/298 = 2529.60 J/K-mol

Part C ) with, dH = 182.6 kJ

dSorxn = (182.6 + 566.62)/298 = 2514.16 J/K-mol

Part D ) with, dH = -77.6 kJ

dSorxn = (-77.6 + 566.62)/298 = 1641.007 J/K-mol

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