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Chem 250 2nd Semester Exam Review Worksheet Part II (answers are at the end of this worksheet) 1. Carbon dioxide is released into the atmosphere through the combustion of octane (C8H18) in gasoline. Write the balanced chemical equation for the combustion of octane and calculate the mass of octane needed to release 5.00 mol CO2. 2. Chloroform (CHCl3), and important solvent, is produced by a reaction between methane and chlorine. CH4(g) + 3Cl2(g) CHCl3(g) + 3HCl(g) How many g CH4 is needed to produce 50.0 g CHCl3? 3. An alkaline battery produces electrical energy according to this equation. Zn(s) + 2MnO2(s) + H2O(l) Zn(OH)2(s) + Mn2O3(s) a) Determine the limiting reactant if 25.0 g Zn and 30.0 g MnO2 are used. b) Determine the mass of Zn(OH)2 produced. 1 4. Pure zirconium is obtained using the two‐step Van Arkel process. In the first step, impure zirconium and iodine are heated to produce zirconium iodide (ZrI4). In the second step, ZrI4 is decomposed to produce pure zirconium. ZrI4(s) Zr(s) + 2I2(g) Determine the percent yield of zirconium if 45.0 g ZrI4 is decomposed and 5.00 g pure Zr is obtained. 5. A sealed flask contains neon, argon, and krypton gas. If the total pressure in the flask is 3.782 atm, the partial pressure of Ne is 0.435 atm, and the partial pressure of Kr is 1.613 atm, what is the partial pressure of Ar in torr? 6. Hot‐air balloons rise because the hot air inside the balloon is less dense than the cooler air outside. Calculate the volume an air sample will occupy inside a balloon at 43.0 oC if it occupies 2.50 L at the outside air temperature of 22.0 oC, assuming the pressure is the same at both locations. 2 7. A sample of nitrogen gas is stored in a 500.0 mL flask at 108 kPa and 10.0 oC. The gas is transferred to a 750.0 mL flask at 21.0 oC. What is the pressure of nitrogen in the second flask? 8. CO is a product of incomplete combustion of fuels. Find the volume that 42 g of CO gas occupies at STP. 9. A 2.00 L flask is filled with propane gas (C3H8) at 1.00 atm and ‐15.0 oC. What is the mass of the propane in the flask? 10. When heated, solid potassium chlorate (KClO3) decomposes to form solid potassium chloride and oxygen gas. If 20.8 g of potassium chlorate decomposes, how many liters of oxygen gas will form at STP? 3 11. What mass of water must be added to 255.0 g NaCl to make a 15.00 percent by mass aqueous solution? 12. How many grams KOH are contained in 64.3 mL 0.0238 M solution? 13. How many mL of 0.400 M HBr solution can be made from 50.0 mL of 8.00 M HBr solution? 14. Calculate the molality of a solution that contains 15.7 g NaCl in 100.0 g H2O. 15. Calculate the freezing point and boiling point of 2.75 m NaOH in water. 4 16. How much heat is absorbed by a 2000 kg granite boulder as energy from the sun causes its temperature to change from 10oC to 29oC? 17. How much heat is evolved when 1255 g of water condenses to a liquid at 100oC? 18. What mass of octane must be burned in order to liberate 5340 kJ of heat? (ΔHcomb = ‐5471 kJ/mol) 19. NO gas and Cl2 gas react according to the equation 2NO + Cl2 2NOCl. Use the following data to determine the rate law for the reaction by the method of initial rates. Also, calculate the value of the specific rate constant. Initial [NO] Initial Rate (mol/L‐min) Initial [Cl2] 0.50 0.50 1.90 x 10‐2 1.00 0.50 7.60 x 10‐2 1.00 1.00 15.20 x 10‐2 5 20. The concentration of reactant A decreases from 0.400 mol/L at time = 0 to 0.384 mol/L at time = 4.00 min. Calculate the average reaction rate during this time period. 21. Calculate Keq for the following equilibrium when [SO3] = 0.0160 M, [SO2] = 0.00560 M, and [O2] = 0.00210 M. heat + 2SO3(g) 2SO2(g) + O2(g) 22. Predict the shift in the equilibrium of the chemical equation in #21 if: a. the volume increases b. the pressure increases c. [O2] decreases d. [SO3] increases e. the temperature decreases Answers: ‐10.2 2.57 x 10‐4 4.00 x 10‐3 0.0859 17.1 34 71.4 73.0 74.8 102.8 16CO2 18H2O k[NO]2[Cl2] left left Units: g g g g g g L2/(mol2 x min) m mL mol/(L x min) 0.152 112 MnO2 g torr 6 1.734 2.68 1.00 x 103 25O2 right kJ kJ oC oC 2.69 1445 right kPa % 4.16 2830 right L 5.70 30,000 6.72 2C8H18 L L