CHEM 113 1st Edition Lecture 2 Outline of Last Lecture II. Spontaneous Processesa. Spontaneous vs. NonspontaneousIII. Spontaneous expansion of a gasIV. The First Law of Thermodynamics and spontaneous changesV. ΔH and spontaneous changesVI. Freedom of Particle MotionVII. Microstates and dispersal of energyVIII. EntropyOutline of Current Lecture IX. The Third Law of ThermodynamicsX. Standard molar entropiesXI. Factors affecting entropya. Temperatureb. Physical statec. Formation of a solutiond. Atomic size and molecular complexityXII. Entropy and structureCurrent LectureI. The Third Law of Thermodynamicsa. A perfect crystal has zero entropy at absolute zeroi. Ssys=0 at 0Kb. A “perfect” crystal has flawless alignment of all its particlesc. At absolute zero, the particles have minimum energy. So there is only 1 microstated. To find the entropy of a substance at a given temperature, we cool it as close to 0K as possible. Then, heat it in small increments, measure q and T, and calculate ΔS for each increment. The sum of these ΔS values gives the absolute entropy at the temperature of interestII. Standard molar entropiesThese 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.a. S° is the standard molar entropy of a substance. Measured for a substance in its standard state in units of J/mol*Ki. The conventions for defining a standard state include:1. 1 bar for pure gases2. 1M for solutions3. The pure substance in its most stable form for solids and liquids4. A temp of 25° C or 298 KIII. Factors affecting entropya. Entropy depends on temperaturei. For any substance, S° increases as temp increasesii. Lower T less freedom of motion fewer microstates lower Siii. Higher T more freedom of motion more microstates higher Sb. Entropy depends on the physical state of a substancei. S° increases as the phase changes from solid to liquid to gasc. The formation of a solution affects entropyi. Entropy of salts and liquids increases in solution1. The entropy of a salt solution is usually greater than that of that solid and of water, but it is affected by the organization of the water molecules around each ionii. Entropy of gasses decreases in solution1. Entropy of a gas is already so high that it decreases when the gas is dissolvedd. Entropy is related to atomic size and molecular complexityi. Remember to compare substances in the same physical stateIV. Entropy and structurea. For larger molecules like hydrocarbons, the entropy increases with increasing chain lengthb. Ring systems have less entropy than the corresponding chainc. These trends only hold for substances in the same physical statei. The effect of physical state dominates the effect of molecular
View Full Document
Unlocking...