Chem 112 Exam 2 Study Guide
Chem 112 Exam 2 Study Guide Chem 112
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This 0 page Study Guide was uploaded by Rebecca Plummer on Sunday February 28, 2016. The Study Guide belongs to Chem 112 at Pennsylvania State University taught by Dr. Raymond Shaak in Spring 2016. Since its upload, it has received 86 views. For similar materials see General Chemistry in Chemistry at Pennsylvania State University.
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Date Created: 02/28/16
Rebecca Plummer Dr Raymond Schaak 28 February 2016 Exam 2 Study Guide Thermodynamic and Electrochemistry Thermodynamics De nition Capable of moving in the forward direction on its own under a given set of conditions 0 The universe tends to move toward disorder entropy Entropy measure of disorder in a system 0 Increase Temperature increase disorder Temperature increases the speed of the molecules which causes the molecules to move in a more random order Increase pressure decrease disorder An increase in pressure pushes the molecules together to reduce the area in which they have to move 0 Increase volume increase disorder When volume is increased the molecules have more room to move 0 Increase number of moles increase disorder When there is more quotstuffquot there is more chaos think of people at a concert 0 Entropy is positive when there are more products than reactants because there is a larger number of moles o Entropy is negative when there are less products because the number of moles decreases 0 When you increase the size of the molecule increase the number of atoms in the molecule the entropy increases 0 The larger the atom the more entropy Gases have more entropy than liquids which have more entropy than solids The entropy of the universe is always positive 0 According to Ludwig Boltsmann s Proposal an increase in microstates number of ways in which a state can be achieved causes an increase in entropy O SklnW Where k is a constant and W is microstates The Third Law of Thermodynamics states entropy of a pure crystalline substance at absolute zero is 0 o This would mean that the entropy is zero and the temperature in kelvins is zero 0 This never actually occurs because crystals can never be 100 pure and you cannot reach 0K 0 Standard Entropy change for a reaction AS 25 C 1atm o AS ZmolesS products Zmoles S reactant When a sample of a gas expands entropy increases 0 When a sample of a gas is compressed entropy decreases Rebecca Pummer Dr Raymond Schaak 28 February 2016 V ASann initial 0 0 Gibbs Free Energy AG 0 AG AH AS 0 Where H is the change in enthalpy and S is the change in entropy 0 Remember to convert AS to k before calculating anything because AG and AH are both in kJmol 0 If AH is negative and AS is positive AG will always be negative and therefore the reaction is spontaneous at all temperatures 0 If AH is positive and AS is negative AG will always be positive and the reaction will never be spontaneous 0 If AH and AS are both negative AG will be negative at low temperatures and positive at high temperatures The reaction will be spontaneous at low temps and nonspontaneous at high temps 0 If AH and AS are both positive AG will be positive at low temperatures and negative at high temperatures The reaction will be nonspontaneous at low temperatures and spontaneous at high temperatures 0 Remember AH refers to enthalpy and a negative value means that the reaction is exothermic and a positive values means the reaction is endothermic AG rxn ZmolesAG fproducts ZmolesAG freacta nts Free Energy and Equilibrium Reactions are always trying to reach equilibrium 0 Minimum free energy is at equilibrium At equilibrium AG 0 Remember AG is not the same as AG at equilibrium because AG is products reactants When AG 0 then AH TAS and T will be the crossover temperature AG AG RTInQ where Q is the reaction quotient When the reaction is at equilibrium then AG RTInK where K is the equilibrium constant When the reaction is at equilibrium AG 0 an0 so k1 When the reaction is not at equilibrium 0 If AG ltO nKgt0 K M be gt1 so the reaction will consist mostly of products and shift to the left to make more reactants o If AG gtO nKlt0 K M be lt1 so the reaction will consist mostly of reactants and shift to the right to make more products Electrochemistry Rebecca Plummer Dr Raymond Schaak 28 February 2016 Redox reactions 0 Oxidation means the element is losing electrons OIL 0 Reduction means the element is gaining electrons RIG 0 When balancing redox reactions you must separate the reaction into an oxidation reaction and reduction reaction 0 Use electrons to balance both sides of the equation o If Oxygens are present you have to add water to the reaction to balance the oxygens Remember in the overall reaction there should be no electrons present on either side so you may have to multiply the equations by the least common factor to eliminate electrons completely 0 Something that is easily reduced is an oxidizing agent 0 Something that is easily oxidized is a reducing agent 0 Use the Table of Standard Reduction Potentials in Water at 25 C to quantify redox reactions 0 In this speci c table the reactions at the top will be oxidizing agents because they are easily reduced These reactions do not react with acids 0 The reactions at the bottom indicate reducing agents and they do react readily with acids These reactions are being oxidized 0 Species down and to the right will be displaced by species up and to the left 0 The numbers to the left at the potentials used to quantify these reactions 0 A Voltaic Cell is a spontaneous chemical reaction that generates electricity the reactions in this cell do not require an outside force to make the substances react o The anode in this cell houses the metal that is being oxidized The metal loses mass The anode has a negative charge 0 The cathode in this cell houses the metal that is being reduced The metal gains mass The cathode has a positive charge 0 The electrons in this cell ow from the anode to the cathode o The salt bridge is needed to keep the solutions electrically neutral and to allow the free ow of ions from the cells 0 The cell diagram notations Copper and Aluminum is Cus u2 aq AFquot aq Als The left side of the double bar willfalways kt the anjode The right side of the double bar will always be the cathode o The equation to nd the potential of the cell is Ecell Ered oni 0 Remember to ip the sign of the reaction potentials if you have to ip the reaction Rebecca Plummer 0 Dr Raymond Schaak 28 February 2016 For example If the equation you have is ZF39aq then you need to use the equation F2g 2e39 ip the 287 to 287 However do not multiple the cell potential value by anything when you multiply the reaction by something like you did with thermochemistry and Aern F2g 2e39 2F39aq and 0 Cell Potential Relates to Spontaneity Free Energy 0 O O O AG nFE Where AG is Gibbs Free Energy at Standard conditions If AG is negative the reaction is spontaneous N is the number of electrons transferred F is Faraday39s Constant which is 96485Jmolv E is the cell potential Cell Potential Relates to Spontaneity of NonStandard Conditions E E RTnFan o This equation is known as the Nernst Equation
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