Testing

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Definition

• Class Demo with hall
• Chemical Equilibrium when the rate of the
  forward and reverse reactions are equal
• Dynamic Reactions at eq never stop
• Equilibrium DOES NOT mean that the amount of
  reactants and products are equal. They have
  reached an unchanging ratio

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Definition

• NaCl (s) ? Na(aq) Cl-(aq)
• (stress all three species are present)
• 2. N2O4(g) ? 2NO2(g)
• Clear Brown
• Cold Hot

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Graphs

• Starting with all reactants (N2O4)
• N2O4(g) ? 2NO2(g)
• 2. Starting with all products (NO2)

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Eq. Constants

• Kc Eq. Constant involving molarity
• a. Molarity
• b. Example 0.50 M
• 2. Kp Eq. Constant involving pressure
• a. Atmospheres
• b. We live at about 1 atm
• Generic Example
• aA bB ? cC dD

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Eq. Constants

• 2O3(g) ? 3O2(g)
• 2NO(g) Cl2(g) ? 2NOCl(g)
• H2(g) I2(g) ? 2HI(g)

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Heterogeneous Eq.

• Def When more than one state is present in an
  equilibrium
• Rule Always exclude solids and liquids from K.
  They are not considered to have a molarity or
  pressure.

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Heterogeneous Eq.

• SnO2(s) 2CO(g) ? Sn(s) 2CO2(g)
• Pb(NO3)2(aq)Na2SO4(aq)?PbSO4(s)
• 2NaNO3(aq)
• Ba2(aq) SO42-(aq) ? BaSO4(s)

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A Note About Water

• Exclude liquid water (often the solvent)
• Keep gaseous water
• Examples
• CO2(g) H2(g) ? CO(g) H2O(l)
• 3Fe(s) 4H2O(g) ? Fe3O4(s) 4H2(g)

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• An example
• CO(g) Cl2(g) ? COCl2(g)
• Kc 4.6 X 109
• Rules
• Kgtgt1 Favors the products
• Kltlt1 Favors the reactants
• K1 Reactants Products

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• Does the following reaction favor the products or
  reactants?
• N2(g) O2(g) ? 2NO(g)
• Kc 1 X 10-30
• For the following reaction, Kc 794 at 298 K and
  Kc 54 at 700 K. Should you heat or cool the
  mixture to promote the formation of HI?
• H2(g) I2(g) ? 2HI(g)

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• If Kc 2.5 X 10-30 for N2(g) O2(g) ? 2NO(g)
  what is Kc for
• 2NO(g) ? N2(g) O2(g)
• What is Kc for
• ½ N2(g) ½ O2(g) ? NO(g)
• 3. If the Kc for N2(g) 3H2(g) ? 2NH3(g) is
  4.43 X10-3, what is Kc for
• 2N2(g) 6H2(g) ? 4NH3(g)

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• A mixture is allowed to reach eq.. At eq., the
  vessel contained 0.1207 M H2, 0.0402 M N2, and
  0.00272 M NH3. What is the equilibrium constant?
• N2(g) 3H2(g) ? 2NH3(g)
• (Ans 0.105)

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• 2. At eq., a vessel contained 0.00106 M NO2Cl,
  0.0108 M NO2, and 0.00538 M Cl2. What is the
  equilibrium constant?
• NO2Cl(g) ? NO2(g) Cl2(g)
• (Ans 0.558)

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• 3. A mixture of 0.00500 mol of H2 and 0.0100
  mol of I2 is placed in a 5.00 L flask and allowed
  to reach eq.. At eq., the mixture is found to be
  HI 0.00187 M. Calculate Kc.
• H2(g) I2(g) ? HI(g)
• (Ans 51)

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• 4. A vessel is charged with 0.00609 M SO3. At
  eq., the SO3 concentration had dropped to 0.00244
  M SO3. What is the value of Kc?
• SO3(g) ? SO2(g) O2(g)
• (Ans 0.0041)

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• 5. 4.00 mol of HI was placed in a 5.00 L flask
  and allowed to decompose. At eq. It was found
  that the vessel contained 0.442 mol of I2. What
  is the value of Kc?
• HI(g) ? H2(g) I2(g)
• (Ans 0.020)

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• An eq. mixture of gases is analyzed. The partial
  pressure of nitrogen is 0.432 atm and the partial
  pressure of hydrogen is 0.928 atm. If Kp is 1.45
  X 10-5, what is the partial pressure of ammonia?
• N2(g) 3H2(g) ? 2NH3(g)

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• At equilibrium, the partial pressure of PCl5 and
  PCl3 are measured to be 0.860 atm and 0.350 atm,
  respectively. If Kp 0.497, what is the partial
  pressure of Cl2?
• PCl5(g) ?? PCl3(g) Cl2(g)

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• 0 ax2 bx c
• x -b \/ b2 4ac
• 2a
• 2x2 4x 1

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• 1. A gas cylinder is charged with 1.66 atm of
  PCl5 and allowed to reach eq.. If the Kp 0.497,
  what are the pressures of all the gases at
  equilibrium?
• PCl5(g) ? PCl3(g) Cl2(g)
• (Ans 0.97 atm, 0.693 atm)
• (briefly discuss partial pressures)

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• 2. A 1.000 L flask is filled with 1.000 mol of
  H2 and 2.000 mol of I2. The Kc 50.5. What are
  the concentrations of all the gases at
  equilibrium?
• H2(g) I2(g) ? 2HI(g)
• (Ans 0.065 M, 1.065 M, 1.87 M)

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Q Reaction Quotient

• Reaction Quotient
• Calculated the same as K, but using initial
  concentrations
• 3. Q lt K shifts to products
• Q K at equilibrium
• Q gt K shifts to reactants

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Q Reaction Quotient

• If you introduce 0.0200 mol of HI, 0.0100 mol of
  H2 and 0.0300 mol of I2 in a 2.00 L flask, which
  way will the reaction proceed to reach
  equilibrium?
• H2(g) I2(g) ? 2HI(g) Kc 51
• (Ans Q 1.3)

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Q Reaction Quotient

• 2. Predict which way the following reaction
  will proceed as it reaches eq. Assume that you
  start with SO3 0.002 M, SO2 0.005 M and
  O2 0.03M.
• 2SO3(g) ? 2SO2(g) O2(g)
• Kc 0.0041
• (Ans Q 0.2)

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Q Reaction Quotient

• Predict which way the following reaction will
  proceed as it reaches eq. Assume that you start
  with NH3 0.002 M, N2 0.005 M and no H2.
  Kc 0.105
• N2(g) 3H2(g) ? 2NH3(g)

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LeChateliers Principle

• Blue Bottle Demo
• 5 grams KOH
• 3 grams Dextrose
• 250 mL of water
• 1 drop methylene blue

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LeChateliers Principle
If a system at eq. is disturbed, it will shift to
relieve that disturbance

• Definition If a system at eq. Is disturbed, it
  will shift to relieve that disturbance

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• N2(g) 3H2(g) ? 2NH3(g)
• Add N2
• Add NH3
• Remove NH3 as it forms
• Remove H2
• N.B. Does NOT apply to solids and liquids. They
  do not appear in the K.
• LiCl(s) ? Li(aq) Cl-(aq)

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• N2(g) 3H2(g) ? 2NH3(g)
• Identify the of moles of gas on either side.
• Show piston drawing
• Increase the volume of the container
• Decrease the volume of the container

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• N2(g) 3H2(g) ? 2NH3(g)
• Increase the pressure of the system
• Decrease the pressure of the system
• Soda example (CO2(aq) ? CO2(g))
• N.B. Adding a noble or inert gas has no effect
  on the eq. Pressure change without a volume
  change.

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• Endothermic Reactions absorb heat from the
  surroundings
• Heat is added (reactants)
• Cooking is an example
• DH
• Exothermic Reactions Release heat
• Give off heat (products)
• Fire is an example
• DH -

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• CO(g) 3H2(g) ? CH4(g) H2O(g)
• DH -206 kJ/mol
• Heat the system
• Cool the system

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• Catalyst
• Examples
• a. Enzymes
• b. Vitamins
• c. Catalytic convertor
• 3. No effect on the position of equilibrium

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• Example 1
• N2O4(g) ? 2NO2(g)
• DH 58 kJ/mol
• Add N2O4
• Remove NO2 as it forms
• Increase the total pressure
• Increase the total volume
• Cool the solution
• Add a catalyst

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• Example 2.
• 2PbS(s) 3O2(g) ? 2PbO(s) 2SO2(g)
• DH -37 kJ/mol
• Add PbS
• Remove SO2 as it forms
• Add O2
• Increase volume
• Decrease the pressure
• Heat the flask

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• Example 3.
• Given the following eqn., how could you promote
  the formation of PCl3 and Cl2?
• PCl5(g) ? PCl3(g) Cl2(g)
• DH 88 kJ/mol

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• Example 4.
• How could you promote the formation of CH4?
• CO(g) 3H2(g) ? CH4(g) H2O(g)
• DH -206 kJ/mol

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• HC2H3O2(aq) H2O(l) ? H3O(aq)
  C2H3O2-(aq)

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• Fe3(aq) SCN-(aq) ? FeSCN2(aq)

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• Co(H2O)62(aq) 4Cl-(aq) 50 kJ/mol
  ? CoCl42-(aq) 6H2O(l)
• (pink) (blue)

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• NaCl(s) ? Na(aq) Cl-(aq)

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• 20a) 1.35 X 105 b) H2S favored
• 22a) 13.3 b) 0.274 c) 0.0349
• Skip (9.5 X 10-31)
• 26) Kp 1/PSO2
• Na2O is a solid, no molarity or pressure
• Kc 10.5
• 30) 66.8, Products favored

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• 0.0535 atm
• 42a. 0.0362 g I2 b) 0.018 g SO2
• 0.13 M
• 46. 0.011 M