CHEM 480 1nd Edition Lecture 4 Outline of Last Lecture I. System vs. SurroundingsII. WorkIII. Transfer of EnergyOutline of Current Lecture I. HeatII. Isothermal Expansion of Perfect GasIII. Heat Capacity, CIV. Molecular interpretation of Heat CapacityCurrent LectureI. Heata. Heat is the transfer of energy resulting in random motion in the surroundingsb. Q < 0 if E leaves systemc. Q > 0 if E is absorbed by the systemII. Isothermal Expansion of Perfect Gasa. Isothermal = constant temperatureb. Perfect gas holds energy kinetically, no PEc. KE = constant and PE = 0 so Esystem = constantd. U = q + W = 0 so q = -WIII. Heat Capacity, Ca. Extensive – if you double the amount, double heat capacityb. C = q/ΔTc. Standardization of Ci. Cs = specific heat capacity1. Intensive2. For water, 4.184 J/g*Kii. Cm = molar heat capacity1. Intensive2. For water, 75.4 J/mol*KIV. Molecular interpretation of Heat Capacitya. Heat capacity of a substance depends on the accessibility of excited energy levelsThese 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.b. When the density of energy states is large, (a), energy arriving as heat can be distributed over the system with little change in population of accessible states => high heat capacityc. When the density of energy states is small, (b), energy arriving as heat must be accommodated by energy levels not previously occupied. This changes the population of accessible states => low heat
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