CHEM 1120 1nd Edition Lecture 29 Outline of Last Lecture I. Defining Entropya. Entropy as energy dispersalb. Molecular MotionII. Chemical Reactions and ΔSOutline of Current Lecture I. Chemical Reactions and ΔSa. 3rd Law of thermodynamicsb. Standard Molar entropiesc. 2nd LawII. Gibbs Free Energy, Ga. G = H – TSIII. Free Energy and TemperatureIV. Free Energy and the Equilibrium constantCurrent LectureI. Chemical Reactions and ΔSa. 3rd Law of thermodynamicsi. Entropy of a pure crystalline substance at absolute zero is 0ii. Straight line when melting or boiling because more microstates existb. Standard Molar entropiesi. Pure substances must have a positive S ii. For pure elements, S does not = 0 iii. Generally, S (gas) > S (liquid) > S (solid)iv. Generally, higher molar mass higher Sv. Generally, more atoms in a molecule higher Svi. ΔS = Sum of S products – sum of S reactantsc. 2nd law: for a spontaneous process ΔS universe > 0i. ΔS universe = ΔS system + ΔS surroundingsii. ΔS surroundings = q surroundings/T = -q system/T = -ΔH rxn/TII. V. Gibbs Free Energy, Ga. G = H – TS b. If ΔG is negative, the forward reaction is spontaneousi. =0, reaction at equilibriumThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.ii. Is positive, reverse reaction is spontaneousc. Standard Free Energy Changesi. Standard state: pure liquids and solids, gases at 1 atm, solutions at 1 M, for elements –> ΔGf = 0d. ΔG equals the maximum useful work that can be done by the system at constant T and P ΔG = w maxIII. Free Energy and Temperaturea. Does ΔG < 0 for spontaneity make sense? Yesi. Most spontaneous reactions are exothermicii. Spontaneous processes tend to have a positive ΔS, that is, -TΔS negativeIV. Free Energy and the Equilibrium constanta. ΔG = ΔG 0 + RTlnQb. Reaction quotient = Q = the value of the equilibrium expression under any conditionsc. Thermodynamics of living systemsi. Many reactions needed for life are not spontaneous1. Building tissue, nerve signals, muscle contraction, oxygen transport2. How? Energy coupling spontaneous reaction drives nonspontaneous
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