Slide 1What is Thermodynamics?Unit of EnergyKinetic & Potential EnergyKinetic & Potential EnergyEnergy FlowSlide 71st Law of ThermoForms of Energy TransferExample ProblemEnthalpyThermochemical EquationsThermochemical EquationsThermochemcial EquationsThermochemcial EquationsThermochemcial EquationsSlide 17Sample ProblemWhere Does the Heat come from for Hrxn?TemperatureCalorimetrySpecific heatSample ProblemConstant Pressure Calorimetry (Exp. 11)Sample ProblemSample ProblemHess’s LawHess’s LawSample ProblemsSample ProblemsStandard Heats, HStandard Heat of Formation, HfThings to Notice about HfDetermining Hrxn from Hf ValuesSample ProblemsSample ProblemsSample ProblemsFood EnergyFood EnergySample ProblemSection 5.8: Fuels (Read on your own)1ThermochemistryChapter 5Chemistry the Central Scienceby: Brown, Lemay, Bursten, Murphy & WoodwardPresented by: Dr. Stacey GuldeWhat is Thermodynamics?Thermodynamics – study of energy and its transformationEnergy – ability to do work, or transfer heat Terms:System – defined part of the universe•Ex: chem rxn b/t H2(g) & O2(g)Surroundings – everything else•Ex: Cylinder, piston & everything beyond2Unit of EnergySI unit = Joule (J)Older units:calorie – energy to raise the temp of 1 g of water by 1 C•1 cal = 4.184 J•Exact or inexact?Calorie – energy from food•1 Calorie = 1000 calories32211smkgJKinetic & PotentialEnergyKinetic energy, Ek – energy of motionThermal energy: energy as a result of temperature & the movement of atoms & molecules4Ek = Jm = mass, kgv = velocity, m/s221mvEkKinetic & PotentialEnergyPotential energy Ep – stored energyResult of position (attraction/repulsion) relative to other objectsChemical energy – energy stored w/in the bonds holding atoms together (released when chemicals react)5EP = Jk = constant 8.99x109 J·m/C2Q = electrical charges, Cd = distance, mdQkQEP21Energy FlowInternal Energy, E – sum of kinetic & potential energy within a system (COMPLEX!)Look at changes in energy, E associated w/processes•Efinal = energy after (end) of process•Einitial = energy before the process6initialfinalEEE Always define ENERGY from the system’s perspectiveSystems that take in (absorbs/gains) energy from the surroundings•E = + (Ef > Ei)Systems that sends out (produces/loses) energy to the surroundings•E =  (Ef < Ei)7initialfinalEEE 1st Law of ThermoFirst Law of Thermodynamics – energy in universe is constant, neither created nor destroyedAka: law of conservation of energyEx: IF surroundings lose energy, then the system must gain the energy80surrsysEEsurrsysEE Forms of Energy Transfer2 basic forms of transfer b/t system & surrounding:1. Heat (or thermal energy), q – result of a difference in temp only•Heat absorbed by system, q is ___ = endothermic•Heat released by system, q is ___ = exothermic2. Work, w – occurs when an object is moved by a force•Work done by the system, w is ___ •Work done on the system, w is ___ 9--++wqE Example ProblemIf the work done to compress a gas is 74 J and 26 J of heat is given off to the surroundings, what is the change in energy of the gas?10q = -26J (lost)w = +74J (on system)Clicker:5.1 wqE JE 48JJE 7426 EnthalpyEnthalpy, H – describes the heat absorbed/lost by a system at constant pressureState function – process independent of path•Ex: Bank account, LocationEnthalpy of reaction Hrxn – heat associated w/a chemical rxnRemember: sign of H indicates heat lost/gained11HpqreactantsproductsHH rx nHThermochemical EquationsThermochemical equation – balanced eq. including the heat of reaction, Hrxn as reactant or product1. Exothermic – heat is lost, thus H is negativeCan consider heat a product•Rewrite within the equation:12kJgOHgOgH 6.483H )(2)()(2rxn222kJgOHgOgH 6.483)(2)()(2222Thermochemical Equations2. Endothermic - heat is gained, H is positiveCan consider heat a reactant•Rewrite within the equation:13kJgOgHgOH 6.483H )()(2)(2rxn222)()(2)(26.483222gOgHgOHkJ Thermochemcial EquationsBe aware:1. Reversing a rxn: rxn going in opposite direction, so H sign changes14Forming water:Decomposing water:kJgOHgOgH 6.483 H )(2)()(2rxn222kJgOgHgOH 6.483 H )()(2)(2rxn222Thermochemcial EquationsBe aware:2. Phases: different phases, different enthalpies15Clicker:5.2-890.0kJH )(2)()(2)(rxn2224 lOHgCOgOgCH-802.0kJH )(2)()(2)(rxn2224 gOHgCOgOgCHThermochemcial EquationsBe aware: 3. Magnitude: H is proportional to the amount of chemicals present•1 mol CH4 produces: ___ mols H2O as well as _______ kJ•2 mols CH4 produces: __ mols H2O as well as ______ kJCreates a mol:heat conversion factor!16-1780-890.024-890.0kJH )(2)()(2)(rxn2224 lOHgCOgOgCH17Sample ProblemHow much heat is released when 4.51g of oxygen gas is reacted with methane, if the enthalpy of reaction is 890.0 kJ?18= - 62.7kJ4.51gHeat ?Clicker: 5.4Mol:HeatClicker: 5.3)(2)()(2)(2224gOHgCOgOgCH  2O 51.4 g 2O mol 12O g 32.002O mols 2kJ 0.890kJ0.890rxnHWhere Does the Heatcome from for Hrxn?When a reaction takes place, reactant BONDS are broken and product BONDS are formedEnergy required to break bondsEnergy released to form bondsSo, if more heat goes in to break bonds than is released when bonds form, then a rxn is endothermic & Hrxn = +1920TemperatureTemperature, T – measures how hot/cold something is relative to another substanceHeat – energy that flows from cold to hot substancesThree temperature scales1. Fahrenheit, F:•Water freezes at 32F and boils at 212F2. Celsius, C:•Water freezes at 0C and boils at 100C3. Kelvin, K – SI unit•AKA – absolute zero scale–0 K is the lowest attainable temp  328.1 CFTT273CKTTCalorimetryCalorimetry – lab process that measures heat flow (qp) during a chemical reactionCalorimeter – device used to observe the temp change of the surroundings and relate back to the systemYou already know: the more you heat an object the higher its temperatureHeat capacity, C – amount of heat