Question
1. What type of intermolecular forces are found in the following? (a) (2 points) Dry ice, CO2 (s) (b) (2 points) Trimethylamine, H3C N CH3 CH3 (c) (2 points) Methylamine, H3C N H H 2. Use the following table: Substance ∆H ◦ f (kJ/mol) S ◦ (J/mol·K) NO(g) 90.4 210.6 O2 (g) 0. 205.07 NO2 (g) 33.1 240.04 (a) (8 points) Calculate the ∆S ◦ of the reaction: 2 NO(g) + O2 (g) −−→ 2 NO2 (g) (b) (4 points) Calcualte the ∆G ◦ of the reaction at 298.15 K. (c) (8 points) Calculate the ∆G ◦ of the reaction at 400 K. 3. Use the following data for carbon disulfide: State ∆H ◦ f (kJ/mol) ∆G ◦ f (kJ/mol) S ◦ (J/(K·mol)) Liquid 87.3 63.6 151.0 Gas 115.3 65.1 237.8 (a) (4 points) What is the Gibbs free energy of the vaporization process at 25 ◦C? (b) (8 points) Calculate the boiling point of carbon disulfide. CHEM 161, Summer 2015 Exam 2 Name: 4. Water has a boiling point of 100 ◦C and an enthalpy of vaporization, ∆H ◦ vap , of 40.68 kJ/mol. (a) (4 points) Assuming ∆H ◦ vap does not change much with temperature, calculate the ∆S ◦ of vaporization. (b) (4 points) The ∆S ◦ of vaporization of most liquids is about 87 J/(mol·K). If this were the ∆S ◦ vap of water, and it had its same ∆H ◦ vap of 40.68 kJ/mol, what would be the boiling point of water, in ◦C? 5. Hydrogen reacts with nitric oxide in the following reaction: 2 H2 (g) + 2 NO(g) −−→ 2 H2O(g) + N2 (g) The following rate data were obtained for different concentrations of the two reactants at a certain temperature: Experiment [H2 ], M [NO], M Initial rate (M/s) 1 0.212 0.136 0.0248 2 0.212 0.272 0.0991 3 0.424 0.544 0.793 4 0.848 0.544 1.59 (a) (4 points) What is the order in H2 ? (b) (4 points) What is the order in NO? (c) (4 points) What is the rate constant, k? 6. Polonium-210 is used in anti-static devices, and has found use in assassinations due to its extreme toxicity and difficulty of detection. Its half-life is 138.4 days. (a) (4 points) What is its decay constant, in d−1 ? (b) (4 points) If a person was suspected to have been poisoned with 210Po, and the body was exhumed 2938 d later to analyze for the element, what percentage would be left? (Hint: assume the original amount to be 100 units). (c) (4 points) A lethal dose of 210Po is 0.100 µg. How many atoms per second will decay? Assume the atomic weight to be 210 g/mol. 7. (8 points) The concentration of a substance that undergoes first-order decay is 0.400 M. After 20 s, the concentration is 0.150 M. What will the concentration be after 60 s? 8. (8 points) The rate consant for a first-order reaction is 4.60 × 10−4 s −1 at 350 ◦C. If the activation energy is 104 kJ/mol, what will be the rate constant at 400 ◦C?
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