Lecture12 - Mon. Sept. 29, 2003 Todays Lecture Energy,...

Info iconThis preview shows pages 1–10. Sign up to view the full content.

View Full Document Right Arrow Icon
Mon. Sept. 29, 2003 Today’s Lecture Energy, Enthalpy, and Thermochemistry • 9.3 Thermodynamics of Gases • 9.4 Calorimetry • 9.5 Hess’ Law • 9.6 Enthalpies of Formation • 9.7/8 Sources of Energy (Omit)
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
– the internal energy of a system can be changed by a flow of heat ( q ) and/or work ( w ): D E = heat + work = q + w • from the system’s point of view: D E can be: D E > 0 E system increases D E < 0 E system decreases heat q > 0 (endothermic) E system increases q < 0 (exothermic) E system decreases
Background image of page 2
work can be: w > 0 E system increases: surroundings perform work on the system w < 0 E system decreases: system performs work on the surroundings • Units of energy: • heat = energy = J work = energy = J • a common type of work in gases: w = -P D V – expansion: work done by the gas (w < 0) – compression: work done on the gas (w > 0) 2 2 s m Kg J =
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
|work| = |F x distance| = |F D h| |w| = |P A D h| D V = V final - V initial = A D h |w| = |P D V| sign convention: w = -P D V Fig. 9.4 F P F PA A = =
Background image of page 4
• gas expansion: V > 0 w < 0 E system decreases (w done by system) • gas compression: V < 0 w > 0 E increases (w done on system) – note that P in P D V refers to the external pressure 1 L atm = 101.3 J
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
• Enthalpy and calorimetry: – Enthalpy (H): H = E + PV • for a process at constant P: E = q p + w = q p - P V – where q p is the heat at constant P q p = E + P V H = E + P V ∴ ∆ H = q p internal energy of the system Pressure exerted on system by surroundings volume of system
Background image of page 6
– Enthalpy is a measure of heat • a change in enthalpy ( D H ) is equal to the amount of heat ( q P ) given off or absorbed at a constant pressure: D H = D E + P D V =q P D H is called heat of reaction • for a chemical reaction: D H = H products - H reactants D H < 0 exothermic : heat is given off D H > 0 endothermic : heat is absorbed
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 8
• 9.3 Thermodynamics of ideal gases:
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 10
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 01/16/2010 for the course CHEM CHEM 121 taught by Professor Peggy during the Spring '09 term at Simon Fraser.

Page1 / 27

Lecture12 - Mon. Sept. 29, 2003 Todays Lecture Energy,...

This preview shows document pages 1 - 10. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online