Equilibrium Concept Review

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					Chemical Systems and
             Learning Goals:
• Explain the concept of dynamic equilibrium,
  using examples of physical and chemical
  equilibrium systems.
• Explain the concept of chemical equilibrium
  and how it applies to the concentration of
  reactants and products in a chemical reaction
  at equilibrium.
• Create and complete an ICE table for an
  equilibrium system.
• Draw graphs of c vs. t to illustrate a chemical
  system approaching equilibrium.
• Use appropriate terminology such as dynamic
  equilibrium, reversible reaction, closed system,
  equilibrium concentrations, phase equilibrium,
  solubility equilibrium, chemical equilibrium,
  equilibrium position
              Dynamic Equilibrium
 • rate of forward reaction = rate of reverse reaction
 • an observable macroscopic property remains constant
                    summer haze

                                             How do the following
                                               images represent
                                             dynamic equilibrium?

Dynamic Equilibrium?
•two kids balanced on a teeter-totter
•player substitutions during a hockey game
•outdoor pool
•indoor pool
•your own idea?
             Consider the following…

  Over time, what happens
    to an open beaker of
  Over time, what happens
    to the water level if we
    cover the beaker?

We can study equilibrium
 under closed systems!
Write an equation to
 describe the equilibrium
What conditions are required for a dynamic
equilibrium to exist?
• reaction is reversible
• closed system

What are the key characteristics of a dynamic

• forward rate = reverse rate
• observable macroscopic property remains constant
           3 types of Equilibrium
1. Solubility Equilibrium
2. Phase Equilibrium
3. Chemical Equilibrium

NaCl(s)   Na+ (aq) + Cl- (aq)
       Chemical Equilibrium

Write an equation to
describe this equilibrium

Initially, N2O4(g) is in the flask. Draw a graph to
illustrate the changes in concentration of R and P as
the system approaches equilibrium.
Does slope = 0 mean the reaction has stopped?
Are the concentrations of R and P equal at equilibrium?
Draw graphs to illustrate how equilibrium can be
reached from either direction.

Use an ICE table to discover how concentration
changes as the system approaches equilibrium.
   Create and complete an ICE table for the following
   chemical system.

If 0.80 mol of HI are placed in a 0.50 L flask, predict how the
concentrations will change as the system approaches
equilibrium. Write algebraic expressions for the [ ] .
Sample Problem 1 (p. 425)

• The initial concentrations of H2(g) and F2(g) are
  2.0 M. What are the equil. conc. of H2(g) and
  HF(g) if the equil. conc. of F2(g) is 0.48 M?
Sample Problem 2 (p. 426)

• A chemist adds 4.0 mol of ammonia gas to a 2.0 L
  sealed container and heats it. Fig 7 shows the
  changes in the amount of NH3(g) observed over time.
  Determine the equil. conc. of N2(g)and H2(g).
• Practice Problems – p. 427 #1-3
            Equilibrium Position
• The relative concentrations of R and P at equilibrium
  is called the equilibrium position.
• Think of running up the down escalator. Can you
  reach a state of dynamic equilibrium at different
  positions on the escalator?
• How does the equil. position relate to the solubility
  of a solute?
• What does a brown haze over a city in the summer
  indicate about the equil. position of this system?
  N2O4(g)        2 NO2(g)
• What happens in the winter?
Equilibrium Position lies…   extent of   reaction is…   arrow
and favours …                reaction

very far to the right,       100%        complete       
to the right,                >50%        reversible
in the middle,               =50%        reversible
neither R or P
to the left,                 <50%        reversible
very far to the left,        <1%         no reaction     NR
  Draw a bar graph to illustrate the relative
  concentrations of R and P for each equilibrium position.
              Dynamic Equilibrium

BEWARE! 3 Common Misconceptions:
1.Concentrations of reactants and products
   are equal @ equilibrium – equilibrium
2. Equilibrium can only be approached from
   1 side
3. The forward and reverse reactions stop @
   equilibrium… Macroscopically there are
   no changes, but what about the molecular
• Define key terms
• p. 428 #1-6

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