1. In the vapour phase acetic acid partially associates into dimers. At a total pressure of 0.2 bar, acetic acid is 92% associated at 25 C and 82% associated at 45 C. Calculate the enthalpy and entropy changes for the reaction. What will be the effect on the dissociation of changing the total pressure?
[Hint: with 100 moles of acetic acid at 25oC you will have 8 moles of monomer and 46 moles of dimer]
2. The electron in the H atom normally resides in the 1s atomic orbital. However, there is some probability that it might also be found in the 2s orbital. Using the Boltzmann distribution, calculate the relative probabilities that these two orbitals will be occupied at (i) room temperature (ca. 298 K) and (ii) 104 K. Hence explain why the electronic contributions to the heat capacity of a substance can usually be ignored.
(spectroscopic transitions between the 1s and 2s orbitals in the H atom occur at a wavelength of 121.6 nm)
3. A buffer solution was made by dissolving 10.0 grams of sodium acetate in 200.0 mL of 1.00 M acetic acid. Assuming negligible volume change upon dissolution, estimate the pH of the acetic acid/sodium acetate buffer solution given the Ka for acetic acid is 1.7 x 10-5.
4. For the reaction Cu + Cl2 CuCl2 determine on which side the equilibrium lies at 298K.
(Hint: This is an electrochemical question. Use Standard Electrode Potentials to determine the equilibrium constant)
5. The e.m.f. of the cell
Pt H2 (1 bar) HCl (a = 1 mol kg-1 AgClAg
is 0.200 V at 25 oC and dE/dT = -8.665 x 10-5 V K-1. Write down the cell reaction and calculate the Gibbs energy, enthalpy and entropy changes for this reaction at 25 oC.
6. Calculate the solubility of lead sulfate in an aqueous solution at 298 K given that the standard reduction potential is -0.36 V.
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