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Lecture

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Department
Chemistry
Course Code
CHM135H1
Professor
Kris Quinlan

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EXAM: 3 hours; 5 short answers, 28 M/C questions
-half of exam is new material (untested)
-other half is units 1 to 4
LECTURE 14
Slide No. Notes
-electrochemistry deals with relationship between chemical
reactions and electricity
-spontaneous reactions can produce electricity and electricity can
cause non-spontaneous reactions to occur
1-Delta S is negative because entropy of gas greater than that of
liquids
-Spontaneity – calculate delta G
-H and O gas both 0
-Therefore spontaneous
-Delta G = Delta H etc. formula
-Both delta H and delta S are negative
-Whenever both signs the same, some temperatures spontaneous
some not
-Reaction becomes non-spontaneous at high temperatures
-To calculate K for the reaction…
-Delta G = -RTInK
-Q = 1/ (P of H2)squared times P of O2 = 1
-Therefore K is greater than one for reaction to go to products
-Therefore answer either E or D
-To actually determine K
-(1000J/kJ)(-474kJ) = (-8.314J/molK)(298K)InK
-K = 1.44x10^83 therefore reaction goes to completion
-Ans: E
-To calculate temperature when reaction non-spontaneous
-Calculate temperature when reaction switches from non-
spontaneous to spontaneous
-Delta G = Delta H – T times delta S with delta G = 0
-Delta H = 2mol(-285.8kJ/mol) = -571.6kJ
-Delta S = 2mol(699.9J/molK) – 2mol(130.6J/molK)
1mol(205J/molK) = -326.4J/K
-T = delta H/delta S = 1751 K
-Reaction is non-spontaneous at temperatures above 1751K
2-LEO: losing electrons is oxidation; GER: gaining electrons is
reduction
-OIL RIG
-overall reaction – electrons cancel out
-
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