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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:. Equilibrium expression, magnitude of K Le Chatelier’s Principle Reaction Quotient

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Big Idea #6

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  1. 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.”

  2. Concepts: • 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

  3. 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)

  4. Equilibrium expression and Kc • 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

  5. Relationship: Kc & Kp • Kc = equilibrium concentrations • Kp = equilibrium pressure (gas systems only) • Kp = Kc(RT) Δn(difference in coefficient gaseous products and reactants)

  6. 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)

  7. 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

  8. Le Chatelier’s Principle Factors that disrupt an equilibrium system: • Change in concentration (adding/removing reactants or products) • Change in volume/pressure (for gas equilibrium) • Change in temperature (endo/exo reactions) Catalyst: allows a system to reach equilibrium more quickly but does not alter the equilibrium.

  9. Basic concepts: Acid-Base chemistry & pH • 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 Kavalues) • 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

  10. 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

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