L20ThermoI145s09r2

L20ThermoI145s09r2 - Lecture 20: First Law of...

Info iconThis preview shows pages 1–7. Sign up to view the full content.

View Full Document Right Arrow Icon
Lecture 20, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University Reading assignment : OGC §12.2-12.3; C&R §17.2 Learning objectives: Understand how a material can exchange energy with its surroundings: as heat as work Understand the first law of thermodynamics Understand how changes in enthalpy are related to: changes in temperature changes in state Understand how heat capacity is related to the bonding, state, and type of a material Lecture 20: First Law of Thermodynamics; Calorimetry 1
Background image of page 1

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

View Full DocumentRight Arrow Icon
Lecture 20, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University add thermal energy U T separation r oscillates about eq’m spacing r 0 U T ; k B T C&R Figs. 2.8b & 17.3 Adding Heat to a Material 2
Background image of page 2
Lecture 20, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University Doing Work on a Material In compressing a material (constant pressure from all directions), … work is done on it by the surroundings … its energy is raised C&R Figs. 2.8b compression Compressing a material raises its energy 3
Background image of page 3

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

View Full DocumentRight Arrow Icon
Lecture 20, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University Heat and work are forms in which energy is transferred between a system and its surroundings The first law of thermodynamics describes the net change in internal energy ∆U of a system q : heat into system• w : work done on system One type of work: change in volume ∆ V surr (= –∆ V sys ) at constant pressure P : Net change in energy of system at constant pressure: U sys = q + w First Law of Thermodynamics [OGC §12.2] w = P ² V surr = P ² V sys U sys = q P + P V surr = q P Ğ P V sys OGC eq.12.3 4
Background image of page 4
Lecture 20, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University Definition of enthalpy H : Change in enthalpy ∆ H of a system is At constant pressure, ∆ P sys = 0 From previous slide, at constant pressure: Rearranging: U sys = q p - P V sys q p H U + PV H sys = ∆ U sys + PV ( 29 sys Enthalpy [OGC §12.3] H sys = ∆ U sys + P sys V sys = ∆ U + P V sys = ∆ U + PV ( 29 P = Æ H P OGC eq.12.7a OGC eq.12.7b = ∆ U sys + P sys V sys + V sys =0 5
Background image of page 5

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

View Full DocumentRight Arrow Icon
Lecture 20, spring 2009 ENGR 145, Chemistry of Materials
Background image of page 6
Image of page 7
This is the end of the preview. Sign up to access the rest of the document.

This document was uploaded on 07/21/2009.

Page1 / 22

L20ThermoI145s09r2 - Lecture 20: First Law of...

This preview shows document pages 1 - 7. Sign up to view the full document.

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