Chapter+17 - Click to edit Master subtitle style Chapter 17...

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Unformatted text preview: Click to edit Master subtitle style 6/6/11 Chapter 17 Equilibrium: The Extent of Chemical Reactions Chemistry The Molecular Nature of Matter and Change Dr. Shamindri M. Arachchige [email protected] Davidson 11 1 Office Hours: Location: Davidson 11 Monday 1:45-5:00 PM Wednesday 1:45-4:15 PM Other hours by appointment 11 6/6/11 Equilibrium: the extent of a reaction In stoichiometry we talk about theoretical yields, and the many reasons actual yields may be lower. Another critical reason actual yields may be lower is the reversibility of chemical reactions: some reactions may produce only 70% of the product you may calculate they ought to produce. Equilibrium looks at the extent of a chemical reaction. Chapter 17 Equilibrium: The Extent of Chemical Reactions 6/6/11 33 Demonstration: 2 Mg(s) + O 2 (g) → 2 MgO(s) Observations: Chapter 17 Equilibrium: The Extent of Chemical Reactions 6/6/11 Chapter 17 Equilibrium: The Extent of Chemical Reactions Evaporation vs. condensation: V a p o r P re s s u re E q u ilib riu m : H O () 2 H O (g ) 2 A system at equilibrium is dynamic on the molecular level; no further net change is observed because changes in one direction are balanced by changes in the other. 44 6/6/11 Chapter 17 Equilibrium: The Extent of Chemical Reactions Reaching equilibrium on the macroscopic and molecular levels of the reaction: N2O4( g ) 2NO2( g ). 55 6/6/11 66 Chapter 17 Equilibrium: The Extent of Chemical Reactions N 2 O 4 /NO 2 System: N 2 O 4 (g) → 2NO 2 (g) P r e s s u r e ( a t m ) Time (s) 1.6 1.2 0.8 0.4 0.0 20 40 60 80 100 NO 2 N O 2 4 N2O4( g ) 2NO2( g ). 6/6/11 77 Chapter 17 Equilibrium: The Extent of Chemical Reactions After about 60 seconds of reaction time: No net production of NO 2 and no net consumption of N 2 O 4 : Rate of consumption of N 2 O 4 = Rate of production of NO 2 How do we explain this? N 2 O 4 (g) → 2NO 2 (g) and 2NO 2 (g) → N 2 O 4 (g) Equilibrium: N 2 O 4 (g) 2NO 2 (g) - rate of forward reaction = rate of reverse reaction - at equilibrium, the amounts of reactants and products do not change over time. There is no net change in amounts. - However, neither the forward or reverse reaction stops. 6/6/11 88 Chapter 17 Equilibrium: The Extent of Chemical Reactions Experiment 1 Experiment 2 Experiment 3 Initial P (atm) Equilibrium P (atm) Initial P (atm) Equilibrium P (atm) Initial P (atm) Equilibrium P (atm) P N 2 O 4 = 1.00 P NO 2 = 0.00 P N 2 O 4 = 0.22 P NO 2 = 1.56 P N 2 O 4 = 0.00 P NO 2 = 1.00 P N 2 O 4 = 0.07 P NO 2 = 0.86 P N 2 O 4 = 1.00 P NO 2 = 1.00 P N 2 O 4 = 0.42 P NO 2 = 2.16 = ) ( ) ( = p ) P ( 2 O N 2 NO 4 2 2 = ) ( ) ( = p ) P ( 2 O N 2 NO 4 2 2 = ) ( ) ( = p ) P ( 2 O N 2 NO 4 2 2 N O (g) 2 4 2NO (g) 2 P r e s s u r e ( a t m ) Time (s) Exp erime nt 1 1 P r e s s u r e ( a t m...
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This note was uploaded on 06/06/2011 for the course CHEM 1036 taught by Professor Amateis during the Spring '08 term at Virginia Tech.

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Chapter+17 - Click to edit Master subtitle style Chapter 17...

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