(-)∆G = ∆H - T∆S(-)(+)Effect of ∆H and ∆SAn exothermic rxn thatspreads energy. Yeah! It will always be spontaneous (∆G <0).Section 9.72Na(s) + 2H2O(l) !2H2(g) + 2NaOH0 mol gas!2 mol gasEnergy Dispersed ∆S > 0Gives off heat ∆H < 0A fool could get this reaction to work.-(-)(+)∆G = ∆H - T∆S(+)(-)An endothermic rxn thatconcentrates energy.This will rxn will never, ever happen spontaneously (∆G >0)Section 9.72H2O (l) + O2(g) !2H2O2(aq)1 mol gas!0 mol gasEnergy concentrated ∆S < 0Requires heat ∆H > 0Effect of ∆H and ∆SLaugh at the fool that tries to get this to work spontaneously.-(+)∆G = ∆H - T∆S(-)(-)An exothermic rxn thatconcentrates energy.As long is the temperature is low,(T∆S smaller than ∆H) it will happen spontaneously.Section 9.7H2O(l) !H2O(s)liquid!solidEnergy concentrates ∆So< 0Gives off heat ∆Ho< 0SLGSLGHEffect of ∆H and ∆S-(+)News flash: Stuff freezes when it’s cold.∆G = ∆H - T∆S(+)(+)An endothermic rxn thatspreads energy.As long is the temperature is high(T∆S larger than ∆H) it will happenSection 9.7H2O(l) !H2O(g)0 mol gas!1 mol gasEnergy Dispersed ∆S > 0Requires heat ∆H > 0SLGSLGHEffect of ∆H and ∆S-(-)News flash: Stuff evaporates when it’s hot.Reaction Spontaneity Summary∆H∆SSpontaneous (∆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∆SAt low temp, ∆G is the same sign as ∆HAt high temp, ∆G is the opposite sign of ∆S,unless ∆S~0, in which case, ∆G is the same sign as ∆HFree Energy (∆G)temperature∆G < 0 rxn spontaneous∆G > 0 rxn non-spon∆H>0∆H>0, ∆S>0rxn works at hi temp++slope = -T∆S(∆S > 0)∆H<0∆H<0, ∆S>0rxn works every time-+slope = -T∆S(∆S < 0)∆H<0, ∆S<0rxn works at lo temp--∆H>0, ∆S<0rxn never works+-Section 9.8Free Energy, Enthalpy and Entropy
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