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Understanding the 1st Law of Thermodynamics: Enthalpy, Heat Capacity, and Adiabatic Changes

Learn about constant pressure heat capacity, Cp vs. Cv, and calculations for CO2 heating. Explore the conceptual and mathematical aspects.

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Understanding the 1st Law of Thermodynamics: Enthalpy, Heat Capacity, and Adiabatic Changes

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  1. CHEM 433 – 9/30/11 III. 1st Law of Thermodynamics (Chapter 2) - Enthalpy, etc. (2.3-2.5) - Constant Pressure Heat Capacity (Cp) - Cp vs Cv - Adiabatic changes (2.6) READ: Keep reading Chapter #2… EXAM Ave = 40.5/50 = 81% (not bad …)

  2. Units on b must be K-1 ! ? ! ?

  3. Calculate H for constant pressure heating of CO2(1 mol) from 25°C to 50°C, assuming: Cp,m constant (= 37.11 J/K mol) Cp,m not constant, a, b, & c below…

  4. What is bigger - Cp or Cv? Why? 1) Conceptual Rationale: What happens when we add some amount of heat (q) to each system below? Const. V Const. p q q w=0 w≠0 T = TV T = TP The upshot … U and therefore T are less for the constant pressure system because the system can (and will) expand. Cp is BIGGER! 2) Mathematical: Can we calculate the difference: (Cp – Cv = …) for an ideal gas ?

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