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Lecture 8

CHEM 1B Lecture 8: Lecture 8 Thermodynamics


Department
Chemistry
Course Code
CHEM 1B
Professor
Craig Murray
Lecture
8

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What%determines%the naturaldirection%of%change?%
Entropy%-measure%of%disorder
Things%tend%to%go%from%order%to%disorder
Energy%&%matter%tends%to%spread%out
Energy%=%mass%x%gravity%x%height%(localized)
Energy%=%1/2%x%mass%x%velocity2%(kinetic%energy)
A%spontaneous%process%can%occur%without%ongoing%outside%
intervention
Spontaneous*
fast*
§
A%nonspontaneous%process%requires%energy%input
Thermodynamics%has%nothing%to%say%about%how%fast%processes%
happen%
Cares%only%about%initial% state,%spontaneity,%but%does%talk%
about%how%long%it'll%take%(more%activation%energy%=%longer%
process)
Entropy%and%the%2nd%Law%of%Thermodynamics
Most%spontaneous%processes%are%exothermic
Spontaneity%is%not%determined%by%enthalpy;%endothermic%
processes%can%also%be%spontaneous%
Ex:%evaporation,%dissolution%of%salts%
The%second%law%of%thermodynamics%-For%any%spontaneous%
process,%the%entropy%of%the%universe%increases%(𝞓Suniv%>%0)
Or%the%entropy%of%an%isolated%system%increases%in%the%
course%of%any%spontaneous%change
Universe%naturally%progresses%from%order%to%disorder;%
greater%dispersal%of%energy
Matter%and%energy%tend%to%disorder;%quantified%by%the%entropy;%S
Entropy%is%a%state%function%
𝞓S%=%Sf%- Si%
§
𝞓S%is%in%J/k
§
Reversible%and%irreversible%processes
Isothermal%(constant%temperature)%expansion%of%ideal%
gases
Ideal%gas%law%-PV%=%nRT
R%is%the%gas%constant%
R%=%8.3145%J/Kmol
R%=%0.08206%%L%atm/Kmol
§
P%=%nRT/V
Free%expansion%Pex%=%0
W%=%-Pex%𝞓V
𝞓U%=%q%+%w%
W%=%0%because%no%pressure%;%𝞓U%=%0
§
𝞓V%=%vf%- vi%
Irreversible%expansion%Pex%<%Pin% (Same%initial%and%final%states%as%
free%expansion)
Wirrev%=%-Pex%𝞓V%%%%%%%%%%%%%%%%%%%%%wirrev%<%0%%%%%%%%,%%%%%%%%qirrev%>%0
Qirrev%=%-wirrev
𝞓U%=%qirrev%+%wirrev% =%0%
Audio 1
Audio%recording%started:%2:01%PM%Friday,%January%27,%2017
Lecture'8:'Thermodynamics
Friday,%January%27,%2017
2:01%PM
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