Download Big Idea 6

Big Idea #6
“Any bond or intermolecular attraction that can
be formed can be broken. These two processes
are in dynamic competition, sensitive to initial
concentration and external perturbations.”
Concepts:
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Equilibrium expression, magnitude of K
Le Chatelier’s Principle
Reaction Quotient
Multistep process ( relationship of equilibrium constant)
Ksp
Common Ion Effect
Acid/Base Equilbria
Buffers
Titration
Equilibrium Review
Key topics:
•Equilibrium expression
•Equilibrium Constant (Kc)
•Gas Equilibrium (Kp)
•Relationship Kc- Kp
•ICE charts (molar relationships)
•Reaction Quotient (Q)
•Le Chatelier’s Principle
•Solubility Constant (Ksp)
Equilibrium expression and Kc
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Coefficients are used as exponents.
Describe concentrations of (aq) and (g) only.
Kc = [products]/[reactants]
Kc > 1 means equilibrium favors forward direction
(formation of product)
• Kc < 1 describes an equilibrium that favors reverse
reaction (formation of reactants)
• Kc =1 system is at equilbrium
Relationship: Kc & Kp
• Kc = equilibrium concentrations
• Kp = equilibrium pressure (gas systems only)
• Kp = Kc(RT) Δn (difference in coefficient gaseous products and reactants)
ICE charts
• Stoichiometric relationship of reactants: products
• Assume reaction occurs in the forward direction.
• Some strategies:
– Perfect square
– Quadratic equation
– 5% rule
(used when K is very small-compared to initial concentration)
Reaction Quotient (Q)
• Used to determine the direction required for a
system to achieve equilibrium.
• Q<K - reaction must move forward
• Q> K – reaction must move in reverse
• Q = K – reaction at equilibrium
Le Chatelier’s Principle
Factors that disrupt an equilibrium system:
1. Change in concentration (adding/removing reactants or
products)
2. Change in volume/pressure (for gas equilibrium)
3. Change in temperature (endo/exo reactions)
Catalyst: allows a system to reach equilibrium
more quickly but does not alter the equilibrium.
Basic concepts:
Acid-Base chemistry & pH
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Recognizing acid/base and conjugate base/acid
Calculation of pH, pOH, [H3O+], [OH-]
Calculating pH for solutions of strong acids/base
Ionization constant: Ka, Kb
Polyprotic acid (and associated Ka values)
pKa, pKb
Acid-Base properties of salts
Predicting direction of acid-base reaction
Types of acid-base reactions
Calculations with equilibrium constants
Titration of acid/base and characteristic titration curves
Titration Curves
Solubility constant (Ksp)
• Remember, expression does not include (s)
salt(s) cation (aq) + anion(aq)
• Common ion effect: presence of an ion at the start of the “reaction”.
Alters the solubility (think Le Chatelier)
• pH and solubility: role of pH may impact the solubility of an
insoluble salt based on the common ion effect (ex. Mg(OH)2
enhances by the presence of H+ ions/acidic)
• Formation of a precipitate- again use Q when Q> Ksp a precipitate
will form