c161l17_10_12b

c161l17_10_12b - Energy calculations Energy Thermochemical...

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Energy calculations Energy calculations W Thermochemical equations relate the number of moles used or produced in a reaction to the energy produced or consumed. W We can treat the enthalpy the same way we treat reactants or products.
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Enthalpy Enthalpy W Δ U = q + w=q - P Δ V W At constant volume Δ V = 0 Δ U = q v = C v Δ T W If we define a new function enthalpy H=U + PV Δ H = Δ U + P Δ V + V Δ P At constant pressure Δ P=0, so Δ H = Δ U + P Δ V =q - P Δ V + P Δ V = q p = C p Δ T
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Properties of Enthalpy Properties of Enthalpy W Enthalpy is a state function Δ H = H final -H initial Cannot measure H, only Δ H W For an exothermic process Δ H<0, for an endothermic process Δ H>0 W Enthalpy is an extensive property Double the amount, double the enthalpy
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Changes of State Changes of State W Vaporization - “Boiling” - changing from liquid to gaseous Always endothermic process Evaporation for cooling Reverse process called condensation W Enthalpy of vaporization amount of energy (at constant pressure) to vaporize a substance Usually expressed as a molar quantity
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Heating curves Heating curves -350 -250 -150 -50 50 150 Heat (q) Temperature ms Δ T ms Δ T n Δ H
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This note was uploaded on 11/12/2011 for the course CHEM 160:161 taught by Professor Siegel during the Fall '09 term at Rutgers.

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c161l17_10_12b - Energy calculations Energy Thermochemical...

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