Popular in Chemistry 0970
Popular in Chemistry
This 6 page Class Notes was uploaded by Angela Chang on Tuesday February 10, 2015. The Class Notes belongs to CHEM 0970 at a university taught by Dr. Morris in Fall. Since its upload, it has received 40 views.
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Date Created: 02/10/15
GradeBuddy Chem 0970 Exam 3 Chem Ch 1820 Entropy and Spontaneous Reaction Gibbs Free Energy Will always be spontaneous if exothermic and increase in entropy If endothermic and decrease in entropy never be spontaneous ever If one of the twoexoendo and increasedecrease in entropyl depends on temperature temperature is the only thing that can be changes deltaH and deltaS are most likely constant given constant volume entropy driven rxnl when entropy increases yet endothermic must increase temperature to make deltaG still be negative if exothermicgood for spontaneity but decrease in entropy spontaneous if decrease temperature make the positive side smaller and negative sidedeltaH larger in comparisonl overall negative deltaG Entropy increases l more ability to spread out Look at side with more moles g or I to see relative changes in entropy Spontaneous does not equal fast rxn 2nOI law of thermodynamicsl entropy of universe increaseseffortlessly if entropy of universe increasesl then spontaneous if entropy is constantchange is ON equilibrium larger delta S faster rate of rxn GradeBuddy careful with kJJ couple a nonspontaneous with a spontaneous rxn both have a same prodreactantl chain Equilibrium and ICE table If gases use partial pressure instead of concentrations 5 and I still do nothing raise to c oef cient powers prodreact no gibbs free energy at equilibriumQK standard conditions1 M and 1 atm if gibbs freegtO klt1 less product favored nonspontaneous will be more reactants presentamost no rxn at all enthalpydeltaH is usually much smaller than entropydeltaS if ionsl think about lattice energy more lattice energy more coulombicelectrostatic force less entropy charge contributes more than radius if covalent thing about atoms Electrochemistry E cell is an intrinsic property Multiplying coef cients by a factor n does not multiply E cell it is still it s original form GradeBuddy Only reversing it s equation will negate it Ered on Oxidation numbers Pure elements are 0 0 2 exception is H20xperoxide 0 1 HD 1 exceptionH alone is 1 Halogens 1 exceptionwith another halogen that is above if or w 0 Sum of chargesnet charge If oxidation increase element is oxidized If oxidation decreases element is reduced Balancing 12 rxns always balance equation stoichiometric coef cients 1 balance 0 with H20 balance H with H balance changes by adding electrons sum up two 12 rxns and make sue electrons are same and on opp sidesred and ox cancel electrons and simplify if it is supposed to be basic add OH to both sides to neutralize H ions into forming water GradeBuddy cancel out waters if both side thing that is oxidizedreducing agent thing that is reducedoxidizing agent galvanicvoltaicl spontaneous EcellgtO higher reduction potential is cathodereduced lower reduction potentialtherefore higher oxidation potential is anodeoxidized electrolytic cell non spontaneous EcellltO lower reduction potential is cathodereduced higher reduction potential is anodeoxidized so that EcellltO requires battery sourceor a voltaic cell in series to fuel it if voltagesemfs are in seriesl Ecell netsum of the 2 E cells Reduced sides will gain in massljl plated by metal Current ows from anode to cathode Group 1Group 2 highly reactive and high oxidation potentials low reduction potentials Anions go to anode Cations go to cathode idqdt Compare moles electrons to moles of compounds using stoichiometric coef cients GradeBuddy Find charge use Faraday s constant n electrons involved must be for the net reactionafter multiplying 12 reactions so electrons cancel Cathodic Protection sacri cial anode Replace with more reactive higher oxidation potential tend to be group 1group2 Will be protected until that anode is used up and completely oxidizedl will plate the cathode reduction occurs Nuclear Not affected by temp pressure or catalysts More likely stable if even protons and even neutrons Less likely stable if odd protons and odd neutrons Radioactivityl spontaneous Zgt83 Large changes in mass Above band of stability neutron rich Beta decay Essentially neutrons converting to protons Below band of stability neutron poor Positron emission because too many protons q or electron capture unlikely Essentially decreasing the protons Equivalent to protons to neutrons Not alpha decayl alpha decay does not change magic number ratios because losing two protons and two neutrons GradeBuddy More frequent if zgt83 and highly unstable want to lose mass Decay Series Nuclear Bombardment with alpha particles nonspontaneous Transmutations Cyclotrons particle accelerators Centripetal magnetic eld Increase in radius bc 2 Dees reverse polarity Activityrate Rate disintegrationstime kl not necessarily SI units can be yearsquot1 as long as t is in years units cancel Half lifel 1St order kineticsindependent of concentration
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