CW17-H&S - H: H rxn = H f (products) - H f...

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CHM 2046/Myers Class Worksheet 17 February 17, 2010 1. Solubility Rules. (A simplified version of text Table 4.1) Group 1A (Na + etc.), NH 4 + and NO 3 - salts are all soluble. +2 and +3 ions with OH - , CO 3 - 2 and S - 2 are not soluble. SO 4 - 2 salts are mostly soluble. Ag + salts are mostly not soluble. 2. NIE for Precipitation Reactions. Ba(NO 3 ) 2 (aq) and Na 2 CO 3 (aq) MgCl 2 (aq) and NH 3 (aq) 3. Complex Ion Equilibria. Fe +3 + SCN - Ni +2 + NH 3 4. Calculation Using Kf: Calculate [Ag + ] for a solution in which [NH 3 ] = 0.10 M and [Ag(NH 3 ) 2 + ] = 0.10 M (both “at equilibrium”). Ag+ + 2 NH 3 Ag(NH 3 ) 2 + , Kf = 1.6 x 10 7 [Ag + ] = ____________ Recall that for AgCl in 0.1 M HCl, [Ag + ] = 1.8 x 10 -9 M (Worksheet 15). Which “removes” Ag+ more effectively from solution, Cl - or NH 3 ? How could this answer possibly change?
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5. Thermodynamics – The study of whether a reaction should go, based on energetics and other factors. A. Energetics: H Calculating
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Unformatted text preview: H: H rxn = H f (products) - H f (reactants) where H f (elements in normal room temperature form) = 0 Predicting the sign of H: Some things that H cant explain ! NH 4 NO 3 (s) NH 4 + (aq) + NO 3-(aq), H rxn = NaCl (s) Na + (aq) + Cl-(aq), H rxn = B. Entropy: S Calculating S: S rxn = S (products) - S (reactants) Predicting the sign of S: S(g) > S(l) S(aq) > S(s) 2 C(s) + O 2 (g) 2 CO(g), S = + 179 J/mol K C(s) + O 2 (g) CO 2 (g), S = 3 J/mol K 2 CO(g) + O 2 (g) 2 CO 2 (g), S = - 173 J/mol K 2 Na(s) + Cl 2 (g) 2 NaCl(s), S = - 129 J/mol K A reaction tends to be spontaneous if H = - and/or S = +. At low T , H is more important. At high T , S is more important....
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CW17-H&S - H: H rxn = H f (products) - H f...

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