Lecture26 - Calorimetry Calorimetry: an experimental method...

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Calorimetry Calorimetry : an experimental method for observing and measuring the flow of heat into and out of a system. The heat measured with constant volume ( q v ) is different from the heat measured with constant pressure ( q p ). The First Law tells us: Δ E = q + w If only PV -work is present, w = P Δ V . Then, Δ E = q P Δ V At constant V , Δ V = 0, thus Δ E = q v .
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Enthalpy ( H ) What is the heat flow at constant P ( q p )? efine a new state function nthalpy = + Define a new state function enthalpy : H E P V Then, the change in enthalpy: Δ H = Δ E + Δ ( PV ) e already know: f only V ork is involved We already know: Δ E = q P Δ V , if only PV -work is involved. Also, Δ ( ) = P Δ V , at constant P . Therefore, Δ H = q P Δ V + P Δ V = q p Heat under constant V Heat under constant P Δ E = q v Δ H = q p Exo thermic Endo thermic Δ H < 0, or Δ E < 0 Δ H > 0, or Δ E > 0 sing energy ining energy losing energy Ä gaining energy
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Heating/Cooling Curve of H 2 O at 1 atm R P
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Δ H of Phase Changes
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This note was uploaded on 07/18/2011 for the course CHEM 154 taught by Professor Hoogendoorn during the Spring '09 term at The University of British Columbia.

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Lecture26 - Calorimetry Calorimetry: an experimental method...

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