7#  .<jjjjĆĜĜĶxj. N$ʼn*ų ʼnrʼnʼnų5ʼnʼnʼnʼnʼnʼnGreat Expectations Sheet I CH142, 1995 1. When 182 grams of gold is added to 22.1 grams of water at a temperature of 25.0 oC the final temperature of the resulting mixture is 27.5 oC. If the heat capacity of gold is 0.129 J/g K, what was the initial temperature of the gold sample? (heat capacity of water is 4.18 J/gK) 2. The standard molar enthalpy change is -905.2 kJ for the oxidation of ammonia: 4 NH3 (g) + 5O2 (g) = 4 NO(g) + 6 H2O(g) Calculate the standard molar enthalpy of formation for ammonia based on the following standard enthalpies of formation: DHf [NO(g)] = +90.3 kJ/mole; and DHf [H2O(g)] = -241.8 kJ/mole. 3. Cyanamide, CH2N2 , is a weak acid that is sometimes used as a fertilizer. A) Calculate the standard enthalpy of formation for cyanamide, given the following standard enthalpies of reaction: CH2N2 (s) + 3/2 O2 (g) = CO2 (g) + H2O(g) + N2 (g) DH1 = -741.4 kJ/mole C(s) + O2 (g) = CO2 (g) DH2 = -393.5 H2 (g) + 1/2 O2 (g) = H2O(g) DH3 = -285.8 B) If 20 grams of cyanamide is reacted with excess oxygen, how much heat will be produced in the reaction? 4. Like all carbonates, barium carbonate can be decomposed to the metal oxide and CO2. BaCO3(s) BaO(s) + CO2(g) If the DHrxn of barium carbonate decomposition is 269.3 kJ/mol, how many kilojoules of heat energy are required to decompose 10.0 g of BaCO3? 5. The dirigible Hindenberg has a gas volume of 1.4 x 108 liters, and was filled with H2. How much energy was released when it burned to gaseous products? (Assume that it was filled to a pressure of 1 atm and 0 oC.) DHf (H2O) = -214 kJ/mol 6. Using the following heats of combustion CH3OH(l) + 3/2O2(g)= CO2(g) + 2 H2O(l) DH = -726.4 kJ C(graphite) + O2(g) = CO2(g) DH = -393.5 kJ H2(g) + 1/2 O2(g) = H2O (l) DH = -285.8 kJ calculate the enthalpy of formation of methanol (CH3OH) from its elements, using the following equation. C(graphite) + 1/2O2(g) + 2H2(g) = CH3OH(l) DH = ? kJ How much heat (in joules) would be produced if 1.00 g of graphite were reacted with excess oxygen and hydrogen to produce methanol? 7. A) How much heat (in joules) is required to convert a 100 cm3 block of solid CO2 into gaseous CO2 (DHsub = 24.2 kJ/mole, density = 1.56 g/cm3)? B) What is the entropy change associated with part a? C) What is the free energy change associated with part a? 8. A) What is the heat of solution of LiCl LiCl(s) + H2O Li+ (aq) + Cl- (aq) DH = ? kJ/mole if the addition of 30g of LiCl to 50 g of water in an perfectly insulated cup results in a temperature increase of 49oC? (assume the sp.ht. of the LiCl solution is 4.0 J/oC g). B) What is the entropy and free energy change associated with part a? For questions 9 - 11 refer to the phase diagram for CO2. 9. Label the three regions of the phase diagram with the appropriate phase (solid, liquid, and gas). 10. Indicate the approximate temperature and nature of each phase change that will occur as you heat a sample of CO2 from -100 to 40 oC at a constant pressure of 20.3 atm. . 11. Label on the figure and define the triple point.  Phase Diagram for CO2 12. The DGfo values for the following gases are given in kJ/mole in parentheses: PH3(+13.4), NH3(-16.4), H2S(-33.6). Which of these three gases is most stable with respect to decomposition into its elements? 13. The reaction shown is at equilibrium. Which of the following changes increases the concentration of products for this reaction? 2 SO2(g) + O2(g)  2 SO3(g) DHo = -200 kJ (a) Adding O2 to the equilibrium mixture (b) Removing SO3 from the equilibrium mixture (c) Adding a catalyst (d) Lowering the temperature 14. (a) Two possible mechanisms for the reaction 2 NO(g) + O2(g) -------> 2 NO2(g) are as follows: i) 2 NO  N2O2 (fast, equilibrium) O2+ N2O2 -------> 2 NO2 (slow) ii) NO + O2 -------> NO2 + O (slow) NO + O --------> NO2 (fast) Predict the rate law to be expected for each of these mechanisms. Show your reasoning. (b) The following experimental results are found for the reaction in (a) at 350 K  Find the rate law and state which of the mechanisms in part (a) is consistent with the experimental findings. 15. From the following kinetics data determine the order of the reaction with respect to B. [A],M [B],M Initial Rate M-1s-1 ------------------------------------------------------------------------ 0.210 0.115 6.30x10-4 0.210 0.230 1.25x10-3 0.420 0.115 2.51x10-3 16. Find the DS for the system, surroundings, and the universe when 25.0 grams of H2O (l) is evaporated at 100 oC, if the heat required is provided by a hot plate at 300 oC. 17. For the chemical reaction Fe3+ (aq) + 3 OH- (aq) = Fe(OH)3 (s) with [Fe3+] = [OH-] = 0.01 M at 298 K, answer each of the following by doing a quantitative calculation of the appropriate thermodynamic function: a) Is this a spontaneous reaction? b) Does the reaction absorb heat? c) Are the products more or less ordered? 18. 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