Lec-03-Chap05-3-bare

Lec-03-Chap05-3-bare - Lec-03-Chap05-3-bare.ppt 9/7/2011...

Info iconThis preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon
Lec-03-Chap05-3-bare.ppt 9/7/2011 Thermochemistry Standard Enthalpies of Reactions 1 Email questions should be submitted to [email protected] . Emails sent to instructors’ personal accounts may be lost . 1 Lec-03: Chemical Thermodynamics Chapter 5 - Continued Deadlines for online quizzes will be on Sat. at 11:00 PM Extensive and Intensive Properties Extensive Properties: their value is proportional to the amount of substance present in the sample. Examples are mass ,volume ,internal energy ,enthalpy , . m V E H etc 2 Intensive Properties: their value is independent of the amount of substance present in the sample. Examples are temperature ,pressure ,density , . T P d etc Notice that by taking the ratio of two extensive properties we obtain an intensive property: m d V mass(extensive) density(intensive) volume(extensive)
Background image of page 1

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

View Full DocumentRight Arrow Icon
Lec-03-Chap05-3-bare.ppt 9/7/2011 Thermochemistry Standard Enthalpies of Reactions 2 Heat Capacity (at constant pressure) Heat capacity: heat exchanged by the system per unit change in its temperature under constant external pressure : 0 is an extensive property; energy it has units of temperat C u J e , , r p p p q H C T C T       specific extensive molar per unit mass per mol intensive intensive p p s p m C n c T c T q T    More convenient are the specific c s or the molar c p heat capacities 3 Heat Capacity (at constant pressure) - continued The specific heat capacity is defined as 0 J heat capacity per unit mass, kg C p s C c m The molar heat capacity is defined as 0 J heat capacity per mol, mol C p p C c n Recall that molar mass mass ps m M n c M c 4
Background image of page 2
Lec-03-Chap05-3-bare.ppt 9/7/2011 Thermochemistry Standard Enthalpies of Reactions 3 Transfer of energy between subsystems m A , T A m B , T B m A , m B , T f Assuming that at contact A and B only exchange energy with each other     pp AB qq  Expressing each q p in terms of the masses, the specific heat capacities, and the changes in temperatures:     A f f ss B TT mm cc 5 Transfer of energy between subsystems - continued sA s A B B f sA sB m c T m c Solving for T f we find 250 g of Al at 97 °C are put in contact with 780 g of Au at 17 °C. What is the final equilibrium temperature? Data: c s (Al)=0.902 J g -1 °C -1 ; c s (Au)=0.128 J g -1 °C -1             97 C 17 C JJ 0.902 0.128 g C g C 0.902 0.128 g 250g 780g 250 CC 0 g g 78 g f T      72.4 C f T  6
Background image of page 3

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

View Full DocumentRight Arrow Icon
Lec-03-Chap05-3-bare.ppt 9/7/2011 Thermochemistry Standard Enthalpies of Reactions 4 Enthalpy Changes: Physical and Chemical Processes For any given transformation: (initial) → (final) ΔH > 0 : the process is endothermic (energy is absorbed from the surroundings) ΔH < 0 : the process is exothermic (energy is released to the surroundings)
Background image of page 4
Image of page 5
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 03/06/2012 for the course CHE 132 taught by Professor Hanson during the Fall '08 term at SUNY Stony Brook.

Page1 / 14

Lec-03-Chap05-3-bare - Lec-03-Chap05-3-bare.ppt 9/7/2011...

This preview shows document pages 1 - 5. Sign up to view the full document.

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