General Chemistry, 5th ed. Whitten, Davis

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General Chemistry, 5th ed.Whitten, Davis Peck

• Definitions
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DIRECTIONS

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  function like flash cards.
• To check your answer, and/or to move on to the
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ACTIVITY (of a component of an ideal mixture)

• A dimensionless quantity whose magnitude is equal
  to molar concentration in an ideal solution,
  equal to partial pressure (in atmospheres) in an
  ideal gas mixture, and defined as 1 for pure
  solids or liquids

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CHEMICAL EQUILIBRIUM

• A state of dynamic balance in which the rates of
  forward and reverse reactions are equal there is
  no net change in concentrations of reactants or
  products while a system is at equilibrium

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DYNAMIC EQUILIBRIUM

• An equilibrium in which processes occur
  continuously, with no net charge

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EQUILIBRIUM CONSTANT, K

• A quantity that indicates the extent to which a
  reversible reaction occurs
• Its magnitude is equal to the mass action
  expression at equilibrium
• K varies with temperature

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HETEROGENEOUS EQUILIBRIA

• Equilibria involving species in more than one
  phase

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HOMOGENEOUS EQUILIBRIA

• Equilibria involving only species in a single
  phase all gases, all liquids, or all solids

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LeCHATELIERS PRINCIPLE

• If a stress (change of conditions) is applied to
  a system at equilibrium, the system shifts in the
  direction that reduces the stress

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MASS ACTION EXPRESSION

• aA bB ? cC dD
• Q (or K at equilibrium) CcDd
• AaBb

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REACTION QUOTIENT, Q

• The mass action expression under any set of
  conditions (not necessarily equilibrium)
• Its magnitude relative to K determines the
  direction in which reaction must occur to
  establish equilibrium

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REVERSIBLE REACTIONS

• Reactions that do not go to completion and occur
  in both the forward and reverse directions

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VANT HOFF EQUATION

• The relationship between ?H0 for a reaction and
  its equilibrium constants at two different
  temperatures
• ln KT2/KT1 (?H0/R)(1/T1 1/T2)
• Or
• log KT2/KT1 (?H0/2.303R) (1/T1 1/T2)

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For any reaction, the value of Kc (equilibrium
constant)

• Varies only with temperature
• Is constant at a given temperature
• Is independent of the initial concentrations

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Q lt K

• Forward reaction predominates until equilibrium
  is established

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Q K

• System is at equilibrium

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Q gt K

• Reverse reaction predominates until equilibrium
  is established

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If a change of conditions (stress) is applied to
a system at equilibrium

• The system responds in the way that best tends to
  reduce the stress in reaching a new state of
  equilibrium
• Concentration changes
• Pressure changes (volume for gas phase)
• Temperature changes
• Introduction of catalysts

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When a new equilibrium is established

• The rates of the forward and reverse reactions
  are equal again
• Kc is again satisfied by the concentrations of
  reactants and products

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A decrease in volume (increase in pressure)

• Shifts the reaction in the direction that
  produces the smaller number of moles of gas

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An increase in volume (decrease in pressure)

• Shifts the reaction in the direction that
  produces the larger number of moles of gas

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If there is no change in the number of moles of
gases in a reaction

• A volume (pressure) change does not affect the
  position of equilibrium

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An increase in temperature

• Favors endothermic reactions

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A decrease in temperature

• Favors exothermic reactions

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?n ?

• ?n (ngas prod) (ngas react)

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Kp ?

• Kp Kc(RT) ?n

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Kc ?

• Kc Kp (RT)- ?n

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For pure solids or liquids

• The activity is taken as 1, so terms for pure
  liquids and pure solids do not appear in the K
  expression for heterogeneous equilibria

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?G0 ?

• ?G0 -RT ln K
• Or
• ?G0 -2.303 RT log K
• R 8.314 J/(molK)

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For equilibria that involve only gases

• The thermodynamic equilibrium constant (related
  to ?G0) is Kp
• For those that involve species in solution, it is
  equal to Kc

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?G0 lt 0 K gt 1

• Products favored over reactants at equilibrium

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?G0 0 K 1

• At equilibrium when CcDdAaBb. (very
  rare

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?G0 gt 0 K lt 1

• Reactants favored over products at equilibrium