Notes
1) The value of the ionization constant, Ka, for hypochlorous acid, HOCl, is 3.2 x 10¯8.
(a) Calculate the hydronium ion concentration of a 0.050-molar solution of HOCl.
(b) Calculate the concentration of hydronium ion in a solution prepared by mixing equal volumes of 0.050-molar HOCl and 0.020-molar sodium hypochlorite, NaOCl.
(c) A solution is prepared by the disproportion reaction below.
Cl2 + H2O ---> HCl + HOCl
Calculate the pH of the solution if enough chlorine is added to water to make the concentration of HOCl equal to 0.0040-molar.
CH3OH(l) + 3/2 O2(g) ---> 2 H2O(l) + CO2(g)
The value of DS° for the reaction above is -80.8 J/mole-degree at 25 °C.
| Substance | DHf°, kJ/mole at 25 °C |
S°, J/mole-degree at 25 °C |
| CH3OH(l) | -238 | 127 |
| H2O(l) | -286 | 69.9 |
| CO2(g) | -393 | 214 |
(a) Calculate DG° for the complete combustion of methanol shown above at 25 °C.
(b) Calculate the value for the equilibrium constant for this reaction at 25 °C.
(c) Calculate the standard absolute entropy, S°, per mole of O2(g).
2 NO(g) + O2(g) <===> 2 NO2(g)
For the reaction above, the rate constant at 380 °C for the forward reaction is 2.6 x 103 liter2/mole2-sec and this reaction is first order in O2 and second order in NO. The rate constant for the reverse reaction at 380 °C is 4.1 liter/mole-sec and this reaction is second order in NO2.
(a) Write the equilibrium expression for the reaction as indicated by the equation above and calculate the numerical value for the equilibrium constant at 380 °C.
(b) What is the rate of the production of NO2 at 380 °C if the concentration of NO is 0.0060 mole/liter and the concentration of O2 is 0.29 mole/liter?
(c) The system above is studied at another temperature. A 0.20-mole sample of NO2 is placed in a 5.0-liter container and allowed to come to equilibrium. When equilibrium is reached, 15 per cent of the original NO2 has decomposed to NO. Calculate the value for the equlibrium constant at the second temperature.
4) Use apppropriate ionic and molecular formulas to show the reactants and the products for the following, each of which results in a reaction occurring in a aqueous solution except as indicated. Omit formulas for any ionic or molecular species that do not take part in the reaction. You need not balance. In all cases a reaction occurs.
(a) Dilute sulfuric acid is added to a solution of barium acetate.
(b) Ammonium chloride crystals are added to a solution of sodium hydroxide.
(c) Solid phosphorus pentachloride is added to excess water.
(d) A solution of hydrogen peroxide is catalytically decomposed.
(e) Powdered iron is added to a solution of iron(III) sulfate.
(f) Chlorine gas is bubbled into a solution of sodium bromide.
(g) A precipitate is formed when solutions of trisodium phosphate and calcium chloride are mixed.
(h) Benzene is treated with bromine in the presence of a catalyst.
5) For the system 2 SO2(g) + O2(g) -----> 2 SO3(g), DH is negative for the production of SO3. Assume that one has an equilibrium mixture of these substances. Predict the effect of each of the following changes on the value of the equilibrium constant and on the number of moles of SO3 present in the mixture at equilibrium. Briefly account for each of your predictions. (Assume that in each case all other factors remain constant).
(a) Decreasing the volume of the system
(b) Adding oxygen to the equilibrium mixture
(c) Raising the temperature of the system
6) The state of aggregation of solids can be described as belonging to the following four types: (1) ionic, (2) metallic, (3) covalent network, or (4) molecular. For each of these types of solids, indicate the kinds of particles that occupy the lattice points and identify the bonding forces among these particles. How could each type of solid be identified in the laboratory?
7) The solubility of Zn(OH)2 is not the same in the following solutions as it is in pure water. In each case, state whether the solubility is greater or less than that in water and briefly account for the change in solubility.
(a) 1-molar HCl
(b) 1-molar Zn(NO3)2
(c) 1-molar NaOH
(d) 1-molar NH3
8) The electron affinities of five elements are given below.
| 13Al | 50 kJ/mole |
| 14Si | 134 kJ/mole |
| 15P | 71 kJ/mole |
| 16S | 201 kJ/mole |
| 17Cl | 364 kJ/mole |
Define the term "electron affinity" of an atom. For the elements listed above, explain the observed trend with the increase in atomic number. Account for the discontinuity that occurs at phosphorus.
9) Write structural formulas for two stable isomers X and Y that have the molecular formula C2H4O2. Select a physical property and a chemical property that would distinguish between the two isomers in the laboratory. Explain.
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