Microstates entropy is also known as a measure of

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MicrostatesEntropy is also known as a measure of randomness.A greater mess means a greater entropy.General Rule: The more available microstates the higher theentropyS= klnWk=Boltzmann constantW= the number of microstatesA single microstate (ln1) means Entropy is 0!
ΔSsys = qsys/TIt takes 6.01 kJ of energy to melt 1mol of ice at 0°CTherefore (1mol)(6.01*103J/mol)/273K =ΔSsys=22 J/KHeat flows into ice and therefore qsys is positiveBecause thermodynamics says that when a system gains energy,the surroundings must lose energy. Thus, you can make morecomplex questions.See next Slide.
Melting 1mol of ice at 0°C on a tabletop at 20°C. Calculate the totalentropy in this situation.
Spontaneous Processes must mean an increase in theentropy of the universe.Δsuniv > 0Some common spontaneity rules:Higher state means more spontaneousGas>liquid>solidMore moles of a gas or liquid on the product sidemeans Δsuniv > 0
ExamplesH2O (l)  H2O (g)>0NH3(g) + HCl(g)  NH4Cl(s)<0Ag+(aq) + Cl-(aq)  AgCl(s)<0C12H22O11(s)  C12H22O11 (aq)>0
Absolute EntropyAbsolute Entropy is for pure substancesStandard Molar Entropy (S°)Calculate the standard entropy change for the following reaction:2H2(g) + O2 (g) 2H2O (g)2(190) – [2(130)+205)]= -85J/KNon-spontaneous
Involving ΔssurrTo calculate Δsuniv we need to sum Δssys and ΔssurrΔSsys is the same as ΔS°ΔSsurr is calculated differently. ΔSsurr is not equal to (-)ΔSsysΔSsurr = ΔHsurr /T= -ΔHsys/TΔHsys = ΔH°
ExampleCalculate Δsuniv:N2(g) + 3H2(g)  2NH3 (g)ΔSuniv = ΔSsys + ΔssurrΔSsys =ΔS°[2(192.5)] – [(191.5)+3(130.6)]= -198.3 J/K
ΔSsurr = ΔHsurr /T= -ΔHsys/TΔHsys = ΔH°[2(-46.1)] – [0 + 3(0)]= 92.2kJ-92.2 * 103 J/ 298K = 309 J/KΔSuniv = ΔSsys + Δssurr-198.3 J/K + 309 J/K = 111 J/K
Gibbs Free Energy (ΔG)Free Energy is the maximum amount of energy available todo workΔG = ΔH – TΔSFundamental Equation for this segment of ThermoΔG < 0 means a process is spontaneous
Standard Free Energy of Formation(ΔG°)ΔG°rxn = Σnproducts ΔG°products – ΣnreactantsΔG°reactantsCalculate the ΔG°ΔG = ΔH – TΔS= -104.9 kJ – 298K(-290.2 J/K)=-104.9 * 103 J – 298K(-290.2 J/K) = -18.4 kJ
Final Example

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