18.29 Consider the decomposition of calcium carbonate: Calculate the pressure in atm of CO 2 in an equilibrium process (a) at 25 o C and (b) at 800 o C. Assume that ΔH o = kJ/mol and ΔS o = J/K. mol for the temperature range.

19.1 (d) 3Br 2 + 6OH   BrO 3  + 5Br  + 3H 2 O

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? min min

Chemical Equilibria How can the yield of NH 3 be maximized? How would the decomposition of NH 3 be maximized? Is this reaction (as written) favored entropically? What is the effect of increasing temperature? Increase [N 2 ] or [H 2 ], decrease [NH 3 ] Increase [NH 3 ], decrease [N 2 ] or [H 2 ] No, ΔS is negative since # moles of gas decrease -TΔS would be positive since ΔS is negative; reaction becomes less spontaneous with increasing T

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. K f = 1/K r and K r = 1/K f Rate of forward reaction equals rate of reverse reaction; no net chemical change

Chemical Equilibria Assume the Haber process proceeds with a ΔG 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?

Colligative properties: freezing point depression Calculate the approximate freezing point of a solution made from 21.0 g NaCl and 1.00 × 10 2 g of H 2 O. K f of water is 1.86°C/m. A. 3.59°C B. 6.68°C C °C D °C E °C The molality would be 2X (van’t Hoff factor, i = 2)

Colligative properties: freezing point depression Calculate the approximate freezing point of a solution made from 21.0 g NaCl and 1.00 × 10 2 g of H 2 O. K f of water is 1.86°C/m. How would having 21.0 g of ethanol (CH 3 CH 2 OH) affect the calculation? How would the calculation be affected if the salt were KNO 3 ? The molality would be 1X, i = 1) The molality would be 2X, i = 2)

Buffers How would you make a buffer of pH 5.0 from acetic acid and sodium acetate? The pK a of acetic acid is 1.74 x 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.

19.31 Nernst equation Calculate the standard potential of the cell consisting of the Zn/Zn 2+ half-cell and the SHE. What will the emf of the cell be if [Zn 2+ ] = 0.45 M, P H2 = 2.0 atm, and [H + ] = 1.8 M? The overall reaction is: Zn (s) + 2H + (aq)  Zn 2+ (aq) + H 2(g) Remember that the oxidant will be the reactant in the half reaction with the more positive reduction potential!