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by: Hazel Medina

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2

# Week 4 Book Notes - Thermal Physics Physics 60

Marketplace > University of California - Irvine > Physics 2 > Physics 60 > Week 4 Book Notes Thermal Physics
Hazel Medina
UCI
GPA 3.0
Thermal Physics
Feng, J.

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With the first midterm fast approaching, I just thought I would get ahead and finish the book notes for this week! Get ready because I will be posting up a study guide very soon! :)
COURSE
Thermal Physics
PROF.
Feng, J.
TYPE
Class Notes
PAGES
2
WORDS
CONCEPTS
thermal physics entropy enthalpy heat engine refrigerator
KARMA
25 ?

## Popular in Physics 2

This 2 page Class Notes was uploaded by Hazel Medina on Monday October 19, 2015. The Class Notes belongs to Physics 60 at University of California - Irvine taught by Feng, J. in Fall 2015. Since its upload, it has received 24 views. For similar materials see Thermal Physics in Physics 2 at University of California - Irvine.

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Date Created: 10/19/15
Physics 60 10172015 Week4 Ch 4 Engines and Refrigerators Ch 41 Heat Engines 0 Heat engine any device that absorbs heat and converts part of that energy into work For example steam turbines However heat engines can only convert part of energy absorbed as heat into work by the heat engine I Heat reservoir where heat is absorbed by the engine temperature Th I Cold reservoir where heat is dumped temperature T 0 Take Qh as heat absorbed from the heat reservoir in a certain period of time Qcas heat expelled to the cold reservoir and W as net work done by the engine Efficiency e E benefitcost WQh To get max efficiency use Qh QC W to replace the W in the cost for efficiency so that it becomes 9 Qh QCQh 1 QCah The second law reveals that QCTc 2 QhTh or QCQh 2 TcTh and the equation becomes e S 1 TcTh To make an engine less efficient than 1 TcTh produce additional entropy that must be disposed by dumping extra heat into the cold reservoir so that there is less energy to convert to work 3 The Carnot Cycle 0 Every engine has a quotworking substance the material that absorbs heat expels waste and does work oftentimes a gas In the process of the gas absorbing heat Q from the hot reservoir the entropy of the reservoir decreases QhTh and entropy of the gas increase QhTgas Since Tgas cannot equal Th imagine Tgas slightly less than Th the gas should be kept at Tgas by letting it expand as it absorbs heat while the gas expands isothermally I We need the heat to compress isothermally o Carnot cycle the cycle of the four steps where 1 isothermal expansion at Th while heat is absorbed 2 adiabatic expansion to Tc 3 isothermal compression at Tc while expelling heat and 4 adiabatic compression back to Th Although maximally efficient minimally probable because of how slow heat moves in the isothermal steps Ch 42 Refrigerators o Refrigerators considered heat engines in reverse Instead of quotefficiencyquot we find coefficient of performance COP benefitcost QcW 39 This time COP QCm 0 1QhQc 1 o This means that QhTh 2 CitTc or Qh QC 2 ThTc leads to COP S 1ThTc 1 TcTh Tc 0 You can get an ideal refrigerator by reversing steps for a maximum efficient heat engine ie reversing the Carnot cycle Ch 5 Free Energy and Chemical Thermodynamics Ch 51 Free Energy as Available Work 0 Enthalpy energy of a system plus energy required to make room for it in environment of constant pressure P H E U PV Have to relate enthalpy to heat I Can do this with Helmholtz free energy F E U TS o F is the energy that must be provided as work to create the system out of nothing therefore F is the available quotfreequot energy Have to relate enthalpy to work I Work done by surroundings to create system in constant pressure P and temperature T Gibbs free energy G E U TS PV Thermodynamic potentials four functions U H F and G I Change in F AF AU TAS Q W TAS where Q is heat added and W is work done on the system 0 Generally AF S W at constant T I Change in G AF AU TAS PAV Q W TAS PAV o W PAV Wother 0 AG S Wother at constant T and P AG AH TAS 339 Electrolysis Fuel Cells and Batteries 0 For electrolysis consider the chemical reaction H20 9 H2 1202 This is the electrolysis of liquid water into hydrogen and oxygen gas 0 Fuel cell that produces electrical work by efficiently expelling waste heat to get rid of excess entropy in the gases Battery similar to a fuel cell but with a fixed internal supply of fuel that is usually not gaseous 339 Thermodynamic Identities o Formulas used when given enthalpy or free energy resemble the thermodynamic identity dU TdS PdV udN H U PV shows that dH dU PdV VdP which becomes dH TdS VdP udN Similarly for F dF SdT PdV udN I S oFoTVN 0 Changing what s fixed P oFoVTN and u oFoN I For G dG SdT VdP udN 5 39dGdTP N V MS3mm l1 dGthy For systems of multiple types of particles udN becomes 2 uidNi I This means that pl oGoN1TpN2 and uz oGoN2TpN2

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