9.7-9.10 - For reactions determine G H and S from...

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1 For reactions, determine G, H, and S from observations A. Nitrogen triiodide Reacts or doesn’t react? Gives off heat or requires heat? Gas formed or consumed? NI 3 (s) ? G < 0 H < 0 G = H - T S (-) (-) (+) Section 9.7 http://www.youtube.com/watch?v=2KlAf936E90 S > 0 For reactions, determine G, H, and S from observations A. Sugar and sulfuric acid Reacts or doesn’t react? Gives off heat or requires heat? Gas formed or consumed? C 6 H 12 O 6 (s) + H 2 SO 4 (aq) ? G < 0 H < 0 G = H - T S (-) (-) (?) S – can’t tell sign could be (+) rxn spontaneous at any temp could be (-) rxn spontaneous only at low temp Section 9.7 http://www.youtube.com/watch?v=6lITtMESI8I&feature=related no concrete evidence Reacts or doesn’t react? Gives off heat or requires heat? B. hydrogen peroxide mixed with water H 2 O 2 (s) ? G > 0 H – can’t tell sign could be (+), but rxn increases disorder(+) could be (-), but rxn decreases disorder(-) could be (+), and rxn decreases disorder(-) S – can’t tell sign could be (+), but rxn is endothermic(+) could be (-), but rxn is exothermic(-) could be (-), and rxn is endothermic(+) rxn will never, ever be spontaneous change temp rxn may work Section 9.7 But with a catalyst: http://www.youtube.com/watch?v=7nxkMrmZepc For reactions, determine G, H, and S from observations Determining G, H, and S from your observations Reacts or doesn’t react? Gives off heat or requires heat? Gas formed or consumed? G < 0 H > 0 G = H - T S (-) (+) (+) S must be (+) Lowering the rxn temp will eventually make the rxn non-spontaneous Section 9.7 A. Bariumhydroxide octahydrate and ammonium thiocyanate Ba(OH) 2 -8H 2 O(s) + 2NH 4 SCN(s) Ba(SCN) 2 (s) + 2NH 3 (aq) + 10H 2 O(l) http://www.youtube.com/watch?v=yTzcoyzPQE0 Looks S ~0 G = G o Unless all chemicals in standard state Chemicals in Standard State (most stable form at 1 atm and indicated temperature) A way to Guess Chemicals in specific mixture in specific reaction conditions Reality Section 9.8 G o < 0, reaction is extensive (prefers product) G o
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