Slide 1First Law of ThermodynamicsThe Energy TaxHeat TaxThermodynamics and SpontaneityReversibility of ProcessComparing Potential EnergyDiamond → GraphiteThermodynamics versus KineticsSpontaneous ProcessesMelting IceSlide 12The Second Law of ThermodynamicsHeat Transfer and Changes in Entropy of the SurroundingsFactors Affecting Whether a Reaction Is SpontaneousEntropySlide 17WMacrostates → MicrostatesMacrostates → MicrostatesMacrostates and ProbabilityEntropy Change in State ChangeEntropy Change and State ChangeEntropy Change in the System and SurroundingsSlide 25Heat Exchange and DSsurroundingsTemperature Dependence of DSsurroundingsQuantifying Entropy Changes in SurroundingsGibbs Free EnergyGibbs Free Energy, DGFree Energy Change and SpontaneityDG, DH, and DSStandard ConditionsThe Third Law of Thermodynamics: Absolute EntropyStandard Molar EntropyStandard Molar EntropyRelative Standard Entropies: StatesRelative Standard Entropies: Molar MassRelative Standard Entropies: AllotropesRelative Standard Entropies: Molecular ComplexitySlide 41Relative Standard Entropies’ DissolutionThe Standard Entropy Change, DSCalculating DGStandard Free Energies of FormationDG RelationshipsWhy Free Energy Is “Free”Free Energy and Reversible ReactionsReal ReactionsDG under Nonstandard ConditionsSlide 51DGº and KSlide 53Why Is the Equilibrium Constant Temperature-Dependent?Chapter 17 Lecture© 2017 Pearson Education, Inc.Lecture PresentationChapter 18Free Energy and Thermodynamics© 2017 Pearson Education, Inc.First Law of Thermodynamics•You can’t win!•The first law of thermodynamics is that energy cannot be created or destroyed.–The total energy of combustion equals the energy that goes to propel the car and the amount dissipated as heat.© 2017 Pearson Education, Inc.The Energy Tax•You can’t break even!•To recharge a battery with 100 kJ of useful energy will require more than 100 kJ because of the second law of thermodynamics.•Every energy transition results in a “loss” of energy.–An “energy tax” demanded by nature–Conversion of energy to heat, which is “lost” by heating up the surroundings© 2017 Pearson Education, Inc.Heat TaxFewer steps generally results in a lower total heat tax.© 2017 Pearson Education, Inc.Thermodynamics and Spontaneity•Thermodynamics predicts whether a process will occur under the given conditions.–Processes that occur without ongoing outside intervention are called spontaneous.•Nonspontaneous processes require energy input to occur.•Spontaneity is determined by comparing the chemical potential energy of the system before the reaction with the free energy of the system after the reaction. –If the system after reaction has less potential energy than before the reaction, the reaction is thermodynamically favorable.•Spontaneity ≠ fast or slow© 2017 Pearson Education, Inc.Reversibility of Process•Any spontaneous process is irreversible because there is a net release of energy when it proceeds in that direction.–It will proceed in only one direction.•A reversible process will proceed back and forth between the two end conditions.–Any reversible process is at equilibrium.–This results in no change in free energy.•If a process is spontaneous in one direction, it must be nonspontaneous in the opposite direction.© 2017 Pearson Education, Inc.Comparing Potential EnergyThe direction of spontaneity can be determined by comparing the potential energy of the system at the start and the end.© 2017 Pearson Education, Inc.Diamond → GraphiteGraphite is more stable than diamond, so the conversion of diamond into graphite is spontaneous. But don’t worry: It’s so slow that your ring won’t turn into pencil lead in your lifetime (or through many of your generations).© 2017 Pearson Education, Inc.Thermodynamics versus Kinetics© 2017 Pearson Education, Inc.Spontaneous Processes•Spontaneous processes occur because they release energy from the system.•Most spontaneous processes proceed from a system of higher potential energy to a system at lower potential energy.–Exothermic•But there are some spontaneous processes that proceed from a system of lower potential energy to a system at higher potential energy.–Endothermic•How can something absorb potential energy, yet have a net release of energy?© 2017 Pearson Education, Inc.Melting IceWhen a solid melts, the particles have more freedom of movement.More freedom of motion increases the randomness of the system. When systems become more random, energy is released. We call this energy, entropy.Melting is an endothermic process, yet ice will spontaneously melt above 0 °C.© 2017 Pearson Education, Inc.Water Evaporating© 2017 Pearson Education, Inc.The Second Law of Thermodynamics•The second law of thermodynamics states for any spontaneous process, the entropy of the universe increases.–DSuniv > 0 •Processes that increase the entropy of the universe occur spontaneously.•Entropy is a state function.•DS = DSfinal – DSinitial© 2017 Pearson Education, Inc.Heat Transfer and Changes in Entropy of the Surroundings•The second law demands that the entropy of the universe increases for a spontaneous process.•Yet processes like water vapor condensing are spontaneous, even though the water vapor is more random than the liquid water.•If a process is spontaneous, but the entropy change of the process is unfavorable, there must have been a large increase in the entropy of the surroundings.•The entropy increase must come from heat released by the system; the process must be exothermic!© 2017 Pearson Education, Inc.Factors Affecting Whether a Reaction Is Spontaneous•There are two factors that determine whether a reaction is spontaneous. They are the enthalpy change and the entropy change of the system.•The enthalpy change, DH, is the difference in the sum of the internal energy and PV work energy of the reactants to the products. •The entropy change, DS, is the difference in randomness of the reactants compared to the products.© 2017 Pearson Education, Inc.Entropy•Entropy is a thermodynamic function that increases as the number of energetically equivalent ways of arranging the components increases, S.–S generally J/molK• –k = Boltzmann constant = 1.38 × 10−23 J/K–W is the number of energetically equivalent ways a system can exist.• Unitless© 2017 Pearson Education, Inc.Salt Dissolving in Water© 2017 Pearson Education,