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Department of Chemistry University of Missouri-St. Louis Name ____________________________________ Chemistry 1111 Practice Exam 3 1. The hybrid molecular orbitals used by the carbon atom in C2H2 are a sp b sp2 c. sp3 d. d2sp3 e. dsp2 2. What bond angle is associated with sp hybrid orbitals? a. 180° b. 90° c. 120° d. 109.5° e. none of the above 3. Which of the following conditions can result in a spontaneous reaction only at low temperatures? a. Δ H > 0, Δ S = 0 b. Δ H > 0, Δ S < 0 c. Δ H < 0, Δ S > 0 d. Δ H < 0, Δ S < 0 e. Δ H > 0, Δ S > 0 4. In total, how many localized bonds and how many lone pairs respectively are there in H2O? a. 2 and 2 b. 4 and 8 c. 4 and 6 d. 2 and 6 e. 2 and 8 5. Which one of the following molecules is polar because of its geometry (which molecule has a dipole moment)? a. SiH4 b. CH4 c. BCl3 d. SF6 e. CHBr3 6. Given: CaCO3(s) → CaO(s) + CO2(g) ΔH0 = 178.0 kJ How much energy would be required to decompose exactly 2 moles of CaCO3(s) 1 a. b. c. d. e. 178.0 kJ 356 kJ -356 kJ 89 kJ -89 kJ 7. The thermochemical equation which defines the enthalpy of formation of acetylene, C2H2(g) is a. 2 C(s) + H2(g) → C2H2(g) b. 2 C(g) + 2H(g) → C2H2(g) c. 2 C2(g) + 2H(g) → C2H2(g) d. C2H6(g) → C2H2(g) + H2 e. none of the above 8. Which of the following has a standard molar enthalpy of formation of zero at 25° and 1 atm pressure? a. CO2(g) b. H2O(l) c. Zn(s) d. NO(g) e. CH4 9. Given the enthalpies of formation of n-hexanol, C6H13OH(l): –377.5; CO2(g): -393.5; and H2O(g): –241.8 kJ/mol, what is the enthalpy change for the combustion of a mol of n-hexanol, to form gaseous CO2 and H2O? a. 3984 kJ b. –3676.1 kJ c. –3984 kJ d. +3676.1 kJ e. –462.1 kJ 10. Calculate the amount of energy required to raise the temperature of a 13.5 gram piece of copper from 25.0 °C to 423 °C. The specific heat of copper is 0.385 J/g °C. 11. Write Lewis dot structures showing the valence electrons for: a. hydrogen sulfide H2S b. ethylene, C2H4 12. Write Lewis dot structures showing the valence electrons for: 2 a. borohydride ion, BH4 – b. ammonium ion NH4+ 14. The relative rates of effusion of H2 to He in an equal molar mixture of both is: a. (2/1)1/2 b. (1/1) 1/2 c. 1/2 d. 2/1 15. Sulfuric acid (H2SO4), the most widely produced chemical in the world, is made by a two-step oxidation of sulfur to sulfur trioxide, SO3, followed by reaction with water. Calculate ΔH0f for SO3 (in kilojoules per mole), given the following data: S(s) + O2(g) → SO2(g) SO3(g) → SO2(g) + ½ O2(g) ΔH0 = -296.8 kJ ΔH0 = +98.9 kJ 16. Assuming that Coca Cola has the same specific heat as water (4.184 J/(g°C), the amount of heat lost when one can (about 350 g) is cooled from 25 °C to 5 °C is: a. -29.3 kJ b. 29.3 kJ c. -36.6 kJ d. -29.3 J e. 36.6 kJ 17. What is the molecular weight of 2 liters of a gas at 25 ° C and 2 atmospheres pressure if the mass of the gas is 36 g? a. b. c. d. e. 220.3 g mol-1 18.5 g mol-1 22 g mol-1 110 g mol-1 not enough information 18. The vaporization of water going from the liquid phase to the gas phase is accompanied by a. a decrease in entropy 3 b. an increase in entropy c. a negative enthalpy d. none of the above 19. At a constant temperature, if the volume of a cylinder is decreased by ½ of its original volume, the pressure in the cylinder will a. remain the same b. will also decrease by ½ c. will double d. will quadruple 20. 20. Draw two different Lewis structures for compounds with the formula: C2H6S Make sure each heavy atom has a complete octet. (use a line to indicate the sharing of two electrons). nonbonding electrons or lone pair electrons need not be shown. 4