CHEM 106 1nd Edition Lecture 8Outline of Last Lecture I. ProteinsII. ChiralityIII. Fatty AcidsIV. Thermodynamics + Entropy of reactionsOutline of Current Lecture II. MicrostatesIII. EntropyIV. Reactions + Spontaneity Current LectureChapter 14: Thermodynamics (continued)Remember from Chapter 7: energy is not continuous on the atomic scale: quantizedMicrostates: a unique distribution of particles among energy levels Ex: consider a coin toss3 separate coins +1 heads -1 tails example 19 in bookHow many microstates are possible? 8 possible microstates (+1 and -1 are most probable) Consider many molecules at particular total energy and constant temperature-energy from translational, rotational, and vibrational motion of all molecules is distributed among all accessible levels in the same way as it is distributed for a single molecule. -at any point in time, total energy of system is same1 mol of particles likely has millions of microstates -each microstate for this system at this temperature has the same overall Boltzmann distributionAir escaping from a tire – finite # of moleculesAvailable space ↑ , temperature is constantTransitional energy levels become more accessiblee.g. transitional energy levels move closer togethermolecules have access to more energy levelse.g. energy is less localized*entropy is never continuous# microstates ↑ entropy ↑Mathematically: S = k ln W S=entropyK=Boltzmann’s constant 1.38 (10-23) J/KW=# microstates14.2 Thermodynamic Entropy Isothermal processes (same temperature)H2O(s) ↔ H2O (l) ↔ H2O (g) -solids have lowest entropiesSolid H2O: molecules in fixed positions, no translational motion, no rotational motion, only vibrationalLiquid H2O: small amount of translational motion, can rotate + vibrate Vapor H2O: no restrictions on any types of motion# microstates ↑ with each stepEntropy (s) ↑ when s → l, l → g, and s → g Entropy is a state function (just like enthalpy) Entropy change only depends on initial + final states of system.ΔSsys = Sfinal – Sinitial Recall heat (q) chapter 5 ΔSsys = qrev / T qrev = entering or leavingT = temperature in KReversible process (qrev) requires no heat transfer between system and surroundingsEx: melting 1 mol ice @ 0°C qrev for melting ice = 6.01 kJ (ΔH of fusion)ΔSsys = 6.01 kJ273 K = 22.0 J/K Entropy change is + entropy ↑ for the systemRemember 2nd law: entropy of universe ↑ for spontaneous processΔSuniverse + ΔSsys + ΔSsurroundingsRemember – isothermal, constant temperatureFor the reverse process, freezing ice @ 0°C qrev = -6.01 kJΔSsurroundings = −601 kJ273 K = -22.0 J/KSo, ΔSuniverse = 0 for isothermal not spontaneousTable 14.1 pg. 670 + Fig. 14.9 pg. 671 -memorizing the two “extremes” is easiestΔSuniverse = ΔSsys + ΔSsurroundings If ΔSsys > 0 and ΔSsurr > 0 then ΔSuniv > 0, spontaneous alwaysIf ΔSsys < 0 and ΔSsurr < 0 then ΔSuniv < 0, not spontaneous -other cases depend on magnitude Pg. 198 q < 0, exothermic q > 0, endothermicConsider an exothermic reaction:qsys < 0 exothermic heat lost to surroundingsqsurr > 0 heat obtained from systemso, ΔSsurr > 0 Process will be spontaneous only if: 1) ΔSsys < 0 2) magnitude of | ΔSsys| < | ΔSsurr| We know that qsys > 0 endothermicAnd we know that qsurr < 0 (had to receive heat from system)NH4NO3 (s) → NH4+ (aq) + NO3- (aq)Remember phase changes Gas has highest standard molar entropyEx: more air added to partially filled balloonEntropy increases because more microstatesS = k ln