CHEM 102 1nd Edition Lecture 10 Outline of Last Lecture I. Calculation ΔS Equations- Example- Natural TendenciesII. Joshua GibbsIII. ΔG Energy Change- ΔG EquationOutline of Current Lecture I. Determining ΔG, ΔS, and ΔHII. Temperature Range of Spontaneity III. Entropy of SurroundingsIV. Predicting Boiling PointsV. Entropy Phase ChangesVI. KineticsCurrent LectureI. Determining ΔG, ΔS, and ΔH- Solid KNO3 dissolves in water at Room Temperature and ΔG is positive; which is trueo ΔG=0o ΔS>0o ΔS<0o ΔG>0 ΔH is positive, you know that because it is given ΔG is negative, you know that because heat is not added to make the KNO3 dissolves ΔS is positive, you know that because heat is not added- You can also use Gibbs Equation- ΔG = ΔH – TΔS- (-) = (+) – (x)- In order for ΔG to be negative ΔS has to be positiveII. Temperature Range of Spontaneity - To find when the equation will change spontaneity, plug in G=0 which means thesolution is in equilibrium right between spontaneity and nonspontaneity- If the equation is following the natural tendencies, then you want the temperature to be above what you calculated in order for it to spontaneousThese 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.o ΔG = ΔH – TΔSo 0 = ΔH – TΔSo T = Δ HΔ S=−150−0.60=250 K ∨−23 ° Co Because S was -0.60, for the equation to be spontaneous, the temperature must be under -23III. Entropy of Surroundings- If ΔG = 0, then TΔS = ΔHo ΔSrxn = QrxnTo ΔSsurr = QsurrTo Qsurr = -Qsys; therefore, ΔSsurr = −ΔHrxnToIV. Predicting Boiling Points- Determine the melting point of solid NaCl where the reaction will be spontaneous- NaCl(s) NaCl(l)- ΔH = 30.3 kJ *** convert to the same units- ΔS = 28.2 J/L ***convert to the same units; 0.0282 kJo ΔG = ΔH – TΔSo 0 = 30.3 – 0.0282xTo 0.0282T = 30.3o T = 1074 K or 801.46 °Co Spontaneous when T > 801V. Kinetics- Kinetic asks the question if this reaction will happen within the given time frame- Kinetics is the study of the rate of the chemical reactiono How fast are reactants used and products formed- Reaction rate: change of concentration of reactant per product per unit of time- Study of mechanisms: sequence of elementary steps that lead to formation of products- React mechanisms: shows how the reaction happens
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