17 Questions on Empirical Formulas of Compounds - Exam 2 | CHEM 1314, Exams of Chemistry

Download 17 Questions on Empirical Formulas of Compounds - Exam 2 | CHEM 1314 and more Exams Chemistry in PDF only on Docsity! per | CHEM 1314 Sections 006-013 Name Key xam 2 October 17, 2007 PLEASE CHECK YOUR LABORATORY SECTION: ___ Section 6; Monday 8:30-10:20 ____ Section 7; Tuesday 8:30-10:20 ___ Section 8; Tuesday 12:30-2:20 ____ Section 9; Tuesday 6:30-8:20 ____ Section 10; Wednesday 8:30-10:20 ____ Section 11; Thursday 8:30-10:20 ____ Section 12; Friday 8:30-10:20 Section 13; Friday 8:30-10:20 INSTRUCTIONS: aaw Be sure your name is on the test and your section checked. This exam consists of 7 total pages. The last contains a periodic table, useful equations, and conversion factors. Make sure you have all pages. You may tear off the last page for convenience. Show your work for full credit. Point values are shown at the end of the problems. Relax and do your best. If you are unsure how to work a particular problem, skip ahead and come back. You have 1 hour, do as much as you can. CHEM 1314 Page 2 Exam 2 1. Given the data in the table below, determine the AH°nm for the following reaction. (10 pts) 2 CH3OH (I) + 3 Oz (g) > 2 CO2 (g) + 420 ()) Substance AH*; (kJ/mol) CH3OH (I} -239 C2HsOH (1) -278 CHsCO2H () -485 CO» (g) -394 H20 (I) -286 AH = AHproducts ~ AHreactants AH = (2 mol CO,)(-394 kJ/mol) + (4 mol H,0)(-286 kJ/mol) -[(2 mol CH30H)(-239 kJ/mol) + (3 mol! ©2)(0 kJ/mol)] = -1454 kJ 2. a) What mass in grams of Mg(OH)z is produced by the reaction of 4.73 g of magnesium with 1.83 g of water? (10 pts) Mg (s) + 2 H20 (I) + Mg(OH)2 (s) + He (g) 4.73 g Mg(1 mol Mg/24.305 g Mg) = 0.1946 mol Mg Excess 4.83 g H2O(1 mol H20/18.02 g H20) = 0.1016 mol H20 LIMITING!!! 0.1016 mol H,O(1 mol Nig(OH)2/2 mol H20)(58.320 g Mg(OH)z!1 mol ivig(OH)2) = 2.96 g Mg(OH): b) When you carried out the above reaction in the lab, you obtained 2.01 g of Mg(OH)2. What is your percent yield? (2 points) % yield = (actual/theoretical) x 100% = (2.01 g/2.96 g) x 100% = 67.9% 3. What is the molarity of a solution prepared by diluting 43.76 mL of a 5.005 M aqueous K;Cr207 solution to 500 mL? (5 pts) MeconeVeone = MaiiVait (5.005 M)(43.76 mL) = Mgi(500 mL) Mai = 0.438 Mi CHEM 1314 Page 5 Exam 2 10. Given the following reactions: Ne (g) + Oz (g) > 2NO g) AH = +180.7 kJ 4 NOs (g) + 4NO (g)+ 2 02 (g) AH = +226.2 kJ What is the enthalpy for the following reaction? (10 pts) 4.NO (g) — 2.NO2(g) + No (g) 2NO —» No + Op AH = -180.7 kJ 2NO +0; — 2NO AH = -113.1 kJ 4NO -» 2NO2 + Ne AH & -293.8 kJ 11. The value of AH’ for the reaction below is -790 kJ. What would be the change in enthalpy for 0.95 g of S? (5 pts) 2S (s) + 302 (9) > 2 SOs (g) 0.95 g S(1 mol S/32.066 g $)(-790 kJ/2 mol S) = -12 kJ 12. Which of the following are decomposition reactions? (3 pts) 1) CH, (g) + O2(g) + CO2(g) + H20 (1) 2) CaO {s) + COz(g) + CaCOs (s) 3) Mg (s) + O2(g) — MgO (s) 4) PbCO3(s) — PbO (s) + CO2(g) A) 1, 2, and 3 B) 4 only C) 1,2, 3, and 4 D) 2and3 E) 2, 3, and 4 13. What is the mass % of C in methane (CH,)? (3 pts) A) 25.13 B) 133.6 C) 74.83 D) 92.26 E) 7.743 14. Label the following reactions as either endothermic or exothermic. (2 pts) A} H20 (I) > H20 (s) exothermic B) H20 (I) — H20 (g) endothermic CHEM 1314 Page 6 Exam 2 all the ane acids. (2 Be) _. (Fi 15. Cage 16. Circle all the strong bases. pts pts NHg Mg(OH)2 17. What is the balanced net ionic equation for the precipitation of CaCO3 when aqueous solutions of Na2COg and CaCl, are mixed? (3 pts) A) 2 Na* (aq) + COs” (aq) — NazCOs (aq) B) 2.Na* (aq) + 2 CI (aq) > 2 NaCl (aq) Cc) Na* (aq) + CF (aq) ~» NaCl (aq) D) Ca™ (aq) + CO;* (aq) — CaCO; (s) E) NazCQ3 (aq) + CaCl (aq) — 2 NaCl (aq) + CaCOs (s) Page2 Page3 Page4 Page5 Page6 EC TOTAL SCORES (27) (19) {24) (23) {7) (6) 100