CH 101 notes 10-19

CH 101 notes 10-19 - Effect of H and S (-) Effect of H and...

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(-) G = H - T S (-) (+) Effect of H and S An exothermic rxn that spreads energy. Yeah! It will always be spontaneous ( G <0). Section 9.7 2Na(s) + 2H 2 O(l) ! 2H 2 (g) + 2NaOH 0 mol gas ! 2 mol gas Energy Dispersed S > 0 Gives off heat H < 0 A fool could get this reaction to work. - (-) (+) G = H - T S (+) (-) An endothermic rxn that concentrates energy. This will rxn will never, ever happen spontaneously ( G >0) Section 9.7 2H 2 O(l) + O 2 (g) ! 2H 2 O 2 (aq) 1 mol gas ! 0 mol gas Energy concentrated S < 0 Requires heat H > 0 Effect of H and S Laugh at the fool that tries to get this to work spontaneously. - (+) G = H - T S (-) (-) An exothermic rxn that concentrates energy. As long is the temperature is low, (T S smaller than H) it will happen spontaneously. Section 9.7 H 2 O(l) ! H 2 O(s) liquid ! solid Energy concentrates S o < 0 Gives off heat H o < 0 S L G S L G H Effect of H and S - (+) News flash: Stuff freezes when it’s cold. G = H - T S (+) (+) An endothermic rxn that spreads energy. As long is the temperature is high (T S larger than H) it will happen Section 9.7 H 2 O(l) ! H 2 O(g) 0 mol gas ! 1 mol gas Energy Dispersed S > 0 Requires heat H > 0 S L G S L G H Effect of H and S - (-) News flash: Stuff evaporates when it’s hot. Reaction Spontaneity Summary H S Spontaneous ( G < 0) -+ always +- never ++ at high T, when |T S| > | H| -- at low T, when | H| > |T S| Section 9.7 Summary G = H - T S At low temp, G is the same sign as H At high temp, G is the opposite sign of S, unless S~0, in which case, G is the same sign as H Free Energy ( G) temperature G < 0 rxn spontaneous G > 0 rxn non-spon H>0 H>0, S>0 rxn works at hi temp + + slope = -T S ( S > 0) H<0 H<0, S>0 rxn works every time - + slope = -T S ( S < 0) H<0, S<0 rxn works at lo temp - - H>0, S<0 rxn never works + - Section 9.8 Free Energy, Enthalpy and Entropy
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Can we predict if a process will occur on its own?
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CH 101 notes 10-19 - Effect of H and S (-) Effect of H and...

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