ETHR 303 Tutorial 5 Solutions - Internal Energy and Enthalpy
Calculating internal energy and enthalpy changes.
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Transcript of Calculating internal energy and enthalpy changes.
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Calculating internal energy and enthalpy changes
![Page 2: Calculating internal energy and enthalpy changes.](https://reader036.fdocuments.net/reader036/viewer/2022062308/56649ce65503460f949b3bdd/html5/thumbnails/2.jpg)
Specific heat function of water vapor
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Ideal gas specific heat
• At low pressures, real gases behave like ideal gas
• Ideal gas specific heat (cv0,cp0) at each given temperature is obtained by extrapolating measured specific heat data at different pressures toward zero pressure.
• Under situations where the gases are nowhere close to condensation (e.g. air/nitrogen/oxygen/helium/hydrogen etc. at atmospheric pressure or lower at room temperature), – the model of “calorically imperfect perfect (ideal) gas” can represent
u and h accurately– so that energy changes can be calculated by:
du=cv0dT, dh=cpodT
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Ideal gas specific heats
Specific heats of monoatomicgases are not functions oftemperatures,u=cvT=3/2RT; h=cpT=5/2RTSince Cp/Cv=k=5/3
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Ways to calculate u and h for calorically imperfect ideal gases
• Definition of specific heat• Specific heat, u and h for ideal gases • Specific heat, u and h for solids and liquids• Use of “Ideal gas properties of” tables (Table A-
17,A-22)• Use of polynomial expressions for specific heat
(Table A-2c)• Use of specific heats tabulated against
temperature (Table A2a-A2b).
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Tables A-17 and A-2