CHem_215_week04_equilibrium-Summer_2011

CHem_215_week04_equilibrium-Summer_2011 - Chapter 17:...

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Unformatted text preview: Chapter 17: Equilibrium 17.1: The equilibrium state and the equilibrium constant 17.2: The reaction quotient and the equilibrium constant 17.4: Reaction direction: Comparing Q and K 17.5: How to solve equilibrium problems 17.6: Reaction conditions and the equilibrium state: Le Chtelier s principle CHEMICAL DYNAMICS CHEMICAL KINETICS Rate (speed) of chemical reaction Reaction mechanism THERMODYNAMICS Spontaneity (direction) of reaction under standard conditions Temperature dependence of spontaneity EQUILIBRIA Extent of reaction Spontaneity (direction) of a specific reaction mixture Dynamic Nature of the Equilibrium State Kinetics applies to the speed of a reaction, the concentration of product appearing (or of reactant disappearing) per unit time. Equilibrium applies to the extent of a reaction, the concentration of product that has appeared given unlimited time, or when no further change occurs. At equilibrium: rate forward = rate reverse 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. Can Q change even when the species being added or removed is not in the expression for Q? Co(H 2 O) 6 2+ (aq) + 4 Cl- (aq) CoCl 4 2- (aq) + 6 H 2 O (l) K eq = [CoCl 4 2- (aq) ] equil [Co(H 2 O) 6 2+ (aq) ] equil [Cl- (aq) ] 4 equil Q = [CoCl 4 2- (aq) ] [Co(H 2 O) 6 2+ (aq) ] [Cl- (aq) ] 4 Does the addition of water change Q for this system? Q can change even when the species being added or removed is not in the expression for Q! Co(H 2 O) 6 2+ (aq) + 4 Cl- (aq) CoCl 4 2- (aq) + 6 H 2 O (l) Q = [CoCl 4 2- (aq) ] [Co(H 2 O) 6 2+ (aq) ] [Cl- (aq) ] 4 Does the addition of water change Q for this system? YES! Q changes upon dilution if n0! Q old = x y z 4 Q new = x/2 y/2 (z/2) 4 Suppose the volume is doubled by adding water: all concentrations are halved. Q new = 16 Q old Q new Q old Does adding or removing a species change K? Co(H 2 O) 6 2+ (aq) + 4 Cl- (aq) CoCl 4 2- (aq) + 6 H 2 O (l) K eq = [CoCl 4 2- (aq) ] equil [Co(H 2 O) 6 2+ (aq) ] equil [Cl- (aq) ] 4 equil Q = [CoCl 4 2- (aq) ] [Co(H 2 O) 6 2+ (aq) ] [Cl- (aq) ] 4 Does the addition of water change K for this system? Adding or removing a species does not change K!...
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CHem_215_week04_equilibrium-Summer_2011 - Chapter 17:...

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