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chap5_23_37

# chap5_23_37 - AAE 439 5.4 THERMOCHEMISTRY BASICS Ch5 23 AAE...

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AAE 439 Ch5 –23 5.4 THERMOCHEMISTRY BASICS

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AAE 439 Ch5 –24 Energies in Chemical Reactions Enthalpy of Combustion (Reactions): Heat of Combustion: – Q CV REACTANTS Stoichiometric fuel-oxidizer (air) mixture at standard state conditions: T ref and p ref . PRODUCTS Complete combustion at standard state conditions: : T ref and p ref . H in = H reactant H out = H product Δ h rxn q CV = h prod h reac Δ H rxn = H prod H reac Δ h C = −Δ h rxn Graphical Interpretation
AAE 439 Ch5 –25 ENTHALPY DEFINITION Absolute Enthalpy Enthalpy for calorically perfect gas. Relative Enthalpy c p is not known at low temperatures. Enthalpy based on reference temperature (25°C). Standard Heat (or Enthalpy) of Formation: Enthalpy of Formation of a substance is the enthalpy change for the formation of one mole of the substance from its elements at standard conditions ( p STD = 1 atm, T STD = 25°C denoted by superscript °). The most stable form of an element at these conditions is referred to as the reference state and is defined as . Heat of Reaction: Hess’s Law uses standard heats of formation to calculate Heat of Reaction for any reaction. Δ H abs = c p dT 0 T Δ H relative = c p dT T ref T Δ H f ° Δ H f ° = 0 Δ H rxn ° Δ H rxn ° = n p Δ H f,products ° n r Δ H f,reactants °

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AAE 439 Ch5 –26 ENTHALPY DEFINITION Heat of Fusion Energy required for the phase change from solid to liquid.
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