CHEM 1415 1nd EditionExam # 3 Study Guide Lectures: 16 - 22Lecture 16 (October 16)Introduction to Energy Energyo Potential Energy Associated with the relative position of an object The higher an object, the more potential energy it contains due to gravity Attraction and repulsion between electrical charges also leads to potential energyo Kinetic Energy Energy associated with motion When an object is falling, it is converting potential energy to kinetic energyKE=12m v2o Internal Energy Combined kinetic and potential energies of the atoms and molecules that make up an objecto Chemical energy Excess energy released if a chemical in bond breaking does not absorb all of the energy Type of potential energyo More specific forms of energy Radiant energy – associated with light or electromagnetic radiation Mechanical energy – movement of macroscopic objects Thermal energy – temperature of an object Electrical energy – moving charges Nuclear energy – released in nuclear fusion and fission processeso Units SI unit – joule(J), 1 J = 1kg m2s2 Heat and Worko Heat Flow of energy between two objects, from the warmer one to the cooler one because of difference in temperatures, process not quantityo Work Transfer of energy accomplished by a force moving a mass in a distance Conservation of Energyo System – part of the universe that is being studiedo Surroundings – remainder of the universeo Boundary – separates the system and the surroundingsoE=q+wo∆ E=Efinal−Einitialo 1st Law of Thermodynamics Energy can be transformed between forms but cannot be created or destroyed Heat Capacity and Calorimetryo Calorimetry A set of techniques that observes heat flow into or out of a systemo Specific heat capacity, c Measures how much heat is required to raise the temperature of one gram of that material by 1℃q=mc ∆ To Heat of formation – the heat change for the production of one mole of a compound from its elements in their standard states Enthalpyo Heat flow under constant pressure conditions, Ho H = E + PVo Exothermic – heat evolves from a system, reaction can be used as a heat source, burning wood, hand warmers are a few examples, ΔH is less than zeroo Endothermic – heat is absorbed by the system, ΔH is greater than zeroo Amount of heat produced = n∗∆ Hphase changeLecture 17 (October 21)Hess’s Law; Heats of Reactions Hess’ Lawo Enthalpy change for any process is independent of the particular way the processis carried out. o State function – variable whose value depends only on the state of the system and not on its historyo∆ Hdesired=∆ HAi+∆ HAfo∆ Hdesired=∆ HBi+∆ HBf Specific Heat o The amount of heat required to raise 1 g of material 1 ℃oc=qm ∆ T∧q=mc ∆ TLecture 18 (October 23)Entropy; Second and Third laws of Thermodynamics Spontaneous Processo Takes place without continuous interventiono May occur quickly or over a long period of time Entropyo Does not depend on a function’s historyo Entropy of 1 mole of gas is usually much greater than one mole of liquid or solido Heating a system increases its entropyo Statistical mechanics – or statistical thermodynamics, used to find a subtle addition to the definition of entropy Second Law of Thermodynamicso In any spontaneous process, the total entropy change of the universe is positive∆ Su>0 and ∆ Su=∆ Ssys+∆ Ssurro Entropy change for the surroundings, ∆ Ssurr=−∆ HTo Thermolysis – advanced recycling or feedstock recycling, recovered monomer canbe purified by distillation or other means Third Law of Thermodynamicso The entropy of a perfect crystal of any pure substance approaches zero as the temperature approaches absolute zero, T=0 ° Ko Impossible to attain a temperature of absolute zeroo Standard molar entropy, S°- determining the change in entropy of a given chemical substance from 0 K to 298 K at pressure of 1 atmo∆ S°=∑iviS°( product )i−∑jvjS°(reactant)jLecture 19 (October 28)Free Energy and Chemical Reactions Gibbs Free Energy, Go A way to predict spontaneous processeso∆ G=∆ H−T ∆ STable 1: possibility of spontaneitySign of ∆ HSign of ∆ SSpontaneityNegative (exothermic) Positive At all temperaturesPositive Negative NeverNegative (exothermic) Negative Only at low temperaturesPositive Positive Only at high temperatureso Exothermic reactions, ∆ H <0, is preferred over endothermic reactionso Reactions where ΔS > 0 are preferredo Enthalpy driven Processes occurring spontaneously at low temperatures Enthalpy term causes ΔG to be negativeo Entropy driven Where the –TΔS term is larger than the ΔH termo Gibb’s free energy is equal to the maximum amount of useful work∆ G=−wmaxo Reversible System is near equilibrium, so a small change in a variable will bring the system back to its initial stateo Irreversible System cannot be restored to initial stateo Standard Gibbs free energy change, ∆ G°- free energy change under these conditions∆ G°=∑iviGi°( product )i−∑jvjGj°(reactant)jLecture 20 (October 30)Rates of Reactions Ozone Depletiono Chapman cycle – proposed by British scientist in 1903 1st step is the photochemical dissociation of O2 to form oxygen atoms,which then react and form ozone, O3 Decrease of ozone concentration over Antarctica and North Americao Ozone is considered a pollutant in the troposphere but beneficial in the stratosphereo Ozone hole isn’t permanent Rates of Chemical Reactionso Reaction rate - ratio of the change in concentration to the elapsed timerate=change∈concentrationelapsed time=∆[substance ]∆ tv∏¿ ∆ t∨rate=−∆ [reactant ]∆t=−∆[reactant ]vreact∆ trate=∆ [ product ]∆ t=∆ [ product ]¿o Average rate – two concentrations are measured at times separated by a finite difference, and the slope of the line between them gives the rate i.e. – traveling 400 miles in 10 hours, avg rate = 40 mpho Instantaneous rate – refers to the rate at a single moment, and it is given by the slope of a line tangent to the curve defined b the change in concentration versus time i.e.- at hour 1, traveling at 54 mph and at hour 4, traveling at 34 mph Rate Lawso Rate Law – mathematical equation showing the dependence of reaction rate on concentration Differential rate law – derived from calculus-Rate=k[X]m[Y]n- The actual values of the
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