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Unformatted text preview: , 223.1 J/mol●K, respectively – Solid C vs. gaseous C: 5.6 vs. 158.1 J/mol●K 10 Even more on entropy! • Generally, larger molecules have larger entropy than smaller molecules – Due to greater molar mass • Molecules with more complex structures have larger entropies than simpler molecules – Since there are more ways for molecule to twist, rotate, vibrate in space • For ex: – CH4, C2H6, C3H8: 186.3, 229.2, 270.3 J/mol•K – Ar, CO2, C3H8: 154.9, 213.7, 270.3 J/mol•K 11 ∆ S°rxn • Calculating standard changes in entropy Similar to calculating ∆ H°rxn • – Don’t forget molar coefficients! ∀∆ S°rxn = S°products ­ S°reactants • All reactants & products in standard states – J/(mol•K) 12 Appendix L, pages A­27­32 • Thermodynamic values: ∆H, ∆S, & ∆G 13 Problem Compute ∆ S°rxn for the following equation: • • 4NH3(g) + 5O2(g) ⇒ 4NO(g) + 6H2O(g) • • • • • Given: 192.8 (J/mol•K) = ammonia 205.2 = oxygen gas 210.8 = nitrogen monoxide 188.8 = water 14 4NH 3(g) + 5O 2(g) ⇒ 4NO(g) + 6H 2O (g) ∆Sorx...
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