Consider the decomposition of calcium carbonate:

1
18.29

• Consider the decomposition of calcium
  carbonate
• Calculate the pressure in atm of CO2 in an
  equilibrium process (a) at 25oC and (b) at 800oC.
  Assume that ?Ho 177.8 kJ/mol and ?So 160.5
  J/K.mol for the temperature range.

2
19.1 (d)
3Br2 6OH? ? BrO3? 5Br? 3H2O
3
Example 14.4

• What is the rate constant for a first order
  reaction that converts 74 of starting material
  to product in 33 minutes?
• What is the half-life of this reaction?

0.0408 min-1
17 min
4
Chemical Equilibria

• How can the yield of NH3 be maximized?
• How would the decomposition of NH3 be maximized?
• Is this reaction (as written) favored
  entropically?
• What is the effect of increasing temperature?

Increase N2 or H2, decrease NH3
Increase NH3, decrease N2 or H2
No, ?S is negative since moles of gas decrease
-T?S would be positive since ?S is negative
reaction becomes less spontaneous with increasing
T
5
Chemical Equilibria

• Write the equilibrium constant expression for the
  reaction in the forward direction.
• Write the equilibrium constant expression for the
  reaction in the reverse direction.
• How are the two equilibrium constants related?
• Describe what is meant by equilibrium in terms of
  chemical change as well as reaction rates.

Kf 1/Kr and Kr 1/Kf
Rate of forward reaction equals rate of reverse
reaction no net chemical change
6
Chemical Equilibria

• Assume the Haber process proceeds with a ?G of
  -33 kJ mol-1 at 298 K. Draw a reaction energy
  diagram showing the relative energies of
  reactants and products as well as the transition
  state.
• Define transition state.
• Define activation energy.
• Define free energy of the reaction.
• What term relates to the equilibrium constant, K?
• What term relates to the rate constant, k?
• What is a catalyst and what parameter is affected
  by the presence of a catalyst?

7
Colligative properties freezing point depression

• Calculate the approximate freezing point of a
  solution made from 21.0 g NaCl and 1.00 102 g
  of H2O. Kf of water is 1.86C/m.
• A. 3.59C
• B. 6.68C
• C. -13.4C
• D. -6.68C
• E. -3.59C

The molality would be 2X (vant Hoff factor, i
2)
8
Colligative properties freezing point depression

• Calculate the approximate freezing point of a
  solution made from 21.0 g NaCl and 1.00 102 g
  of H2O. Kf of water is 1.86C/m.
• How would having 21.0 g of ethanol (CH3CH2OH)
  affect the calculation?
• How would the calculation be affected if the salt
  were KNO3?

The molality would be 1X, i 1)
The molality would be 2X, i 2)
9
Buffers

• How would you make a buffer of pH 5.0 from acetic
  acid and sodium acetate? The pKa of acetic acid
  is 1.74 x 10-5.

Combine equal volumes of 1.74 M sodium acetate
and 1.0 M acetic acid.
Take acetic acid and titrate it with NaOH until a
pH of 5.0 is reached.
10
19.31 Nernst equation

• Calculate the standard potential of the cell
  consisting of the Zn/Zn2 half-cell and the SHE.
  What will the emf of the cell be if Zn2 0.45
  M, PH2 2.0 atm, and H 1.8 M?

The overall reaction is Zn(s) 2H(aq) ?
Zn2(aq) H2(g)
Remember that the oxidant will be the reactant in
the half reaction with the more positive
reduction potential!