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CHM135H1 (333)

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Kris Quinlan

EXAM: 3 hours; 5 short answers, 28 MC 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 - (1000JkJ)(-474kJ) = (-8.314JmolK)(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(-285.8kJmol) = -571.6kJ - Delta S = 2mol(699.9JmolK) 2mol(130.6JmolK) 1mol(205JmolK) = -326.4JK - T = delta Hdelta 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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