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18.29

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 Δ H o = 177.8 kJ/mol and Δ S o = 160.5 J/K . mol for the temperature range. 19.1 (d).

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18.29

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  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 ΔHo = 177.8 kJ/mol and ΔSo = 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, ΔS is negative since # moles of gas decrease -TΔS would be positive since ΔS 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 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?

  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 1.86°C/m. A. 3.59°C B. 6.68°C C. -13.4°C D. -6.68°C E. -3.59°C The molality would be 2X (van’t 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 1.86°C/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!

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