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chemical equilibrium
the rates of the forward and reverse reactions are equal and the concentrations of the reactants and products remain constant
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equilibrium constant
- K = products over reactants raised to the power of their coefficients
- it is a dimensionless quantity(unlike little k), don't worry about why
- constant values unless temperature changes
- If K<<1 - the denominator is much larger than the numerator, therefore the reactants are favored
- If K >> 1 the equilibrium "lies to the right"
- if you flip the reaction, invert K (4.0 --> 0.25)
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homogeneous equilibria
- all reacting species are in the same phase
- all are gasses
- all are aqueous
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heterogeneous equilibria
- reacting species exist in different phases
- solids & gases
- solids & liquids
- don't include solids (s) and liquids (l) in the equilibrium constant only gases (g) or solutions (aq)
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relationship between Kc and Kp
- PV = nRT......so
- Kp = Kc (RT)^ (to the power of the change in n)
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Dynamic Equilibrium
in a reversable reaction reactants are always turning into products and products are always turning into reactants
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Le Chatelier's Principle
- if an external stress is applied to a system at equilibrium, the system adjusts in such a way that the stress is partially offset
- *if adding a gas that doesn't appear in the balanced equation, it has no effect on equilibrium
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law of mass action
for a reversible reaction at equilibrium and a constant temperature, a certain ratio of reactant and product concentrations has a constant value (K)
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multiple equilibria
if a reaction can be expressed as the sum of 2 or more reactions, the equilibrium constant for the overall reaction is given by the product of the equilibrium constants of the individual reactions (Hess's law) Kc = Kc' x Kc"
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catalyst
- lowers the activation energy for the forward and the reverse reaction to the same extent
- doesn't alter the equilibrium constant, nor shifts the equilibrium
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How does temperature affect equilibrium?
- temperature increase favors an endothermic reaction (+^H) - reactants + heat <=> products
- temperature decrease favors an exothermic reaction (-^H) - reactants <=> products + heat
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reaction quotient Q
- same form as K but is not at equilibrium
- if Q < K the reaction must go forward (to the right) (form products) to reach equilibrium
- if Q = K the reaction is at equilibrium
- if Q > K the reaction must go backward (left, reactants) to reach equilibrium
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