Chemistry 200: General Chemistry I - Lecture

Transcription

1 Name Date Chemistry 200: General Chemistry I - Lecture Exam #3, 100 Points Total Form: A Read all directions carefully. Answers not conforming to the directions will be marked as incorrect! Section 1: Matching (10 points) Match the following concepts with the appropriate definitions or examples listed below. Make selections such that each term has its best possible match. Indicate your choices by marking your Scantron sheet (1-10) with the appropriate two-letter code. pascal % yield strong acid q < 0 state function electrolyte interhalogen compounds hydronium endothermic P total = P 1 + P 2 + P P n CE. SI unit for pressure BE. exothermic AC. expresses efficiency of a reaction AD. an acid that completely ionizes in solution AB. covalent compounds between Group 17 elements CD. value does not depend on path AE. (H 2 O)H + or H 3 O + or H + BD. heat used as a reactant in a reaction DE. Dalton s Law of Partial Pressures BC. e.g. NaCl 1

2 Section 2: Multiple Choice (40 points) Choose the term or phrase that best completes the sentence or answers the question. Indicate your selection by marking the appropriate letter on your Scantron sheet. 11. What is the enthalpy change for the reaction Hg (l) + 2Ag + (aq) Hg2+ (aq) + 2Ag (s) if the Hf for the silver(i) ion is kj/mole and the H f for the mercury(ii) ion is kj/mole? kj kj kj kj 12. Generally, halogens are in redox reactions. inert neutralized oxidized reduced 13. If 0.1 mole NaCl reacts with 0.2 mole AgNO 3, then the limiting reactant would be. AgCl AgNO 3 NaCl NaNO A student wants to prepare 25 0 ml of 0.10 M NaCl (MW = 58.4 g/mole) solution. Which procedure is most appropriate? Add 5.8 g of NaCl to 25 0 ml of H 2 O. Add 1.5 g of NaCl to 25 0 ml of H 2 O. Dissolve 5.8 g of NaCl in 50 ml of H 2 O and dilute to 25 0 ml. Dissolve 1.5 g of NaCl in 50 ml of H 2 O and dilute to 25 0 ml. 2

3 15. What does q P represent? heat measured under constant pressure conditions heat heat pressure pressure heat capacity constant 16. When bonds are broken, energy is. absorbed released created destroyed 17. If 1.0 mole N 2 has T = 200 K, to what temperature must a 2.0 mole sample of N 2 be heated in order to have the same KE as the 1.0 mole sample? 100 K 200 K K 400 K 18. If a beaker containing a reaction feels hot, then the reaction is. exothermic kinetic endothermic exergonic 19. A mixture containing 9 moles of F 2 and 4 moles of S is allowed to react according to the equation 3F 2 + S SF 6. How many moles of F 2 REMAIN after 3 moles of S have reacted?

4 20. When a carbon-containing compound undergoes combustion, all of the carbon becomes. solid carbon methane (CH 4 ) carbon dioxide carbonate 21. Ionic compounds dissolve because. ion-ion attractions > water-ion attractions water-ion attractions < ion-ion attractions water-water attractions > ion-ion attractions water-ion attractions > ion-ion attractions 22. At constant temperature, if external pressure increases, then gas volume. decreases increases doubles is inverted 23. Which of the following is the strongest oxidizing agent? Cl Na MnO 4 BrO 24. Calculate H for the chemical reaction Cl 2(g) + F 2(g) 2ClF (g) given the following bond energies: F-F, 159 kj/mole; Cl-Cl, 243 kj/mole; Cl-F, 255 kj/mole kj -108 kj +171 kj +912 kj 4

5 25. Which of the following would be the strongest electrolyte? LiBr CO CdS Cu 26. Avogadro s Law states that when the moles of gas increases, the. T increases V increases V decreases P decreases 27. The Born-Haber cycle cannot be applied to. Li 2 O NaCl CSe 2 CaF Under STP conditions, 1 mole of a gas occupies L 25 C 22.4 L 1 atm 29. The standard enthalpy of formation, Hf, for NO 2 is the enthalpy change for which reaction? N (g) + 2O (g) NO 2(g) 1/2 N 2(g) + O 2(g) NO 2(g) 1/2 N 2 O 4(g) NO 2(g) NO (g) + 1/2 O 2(g) NO 2(g) 5

6 30. The correct name for HIO 3(aq) is. hydrogen iodate iodic acid hydroiodic acid hydrogen iodous acid 6

7 Section 3: Long Answer (10 points each) 31. Neon and argon gas are being collected over water at 30.0 C into an evacuated roundbottom flask. If the total pressure in the flask after the collection is torr, and if it s determined that there are g of Ne and g of Ar in the flask, calculate P Ne and P Ar in units of atm. Note that the vapor pressure of water at 30.0 C is 31.8 mmhg. 7

8 32. 6 points. Clearly identify the oxidation states of every element in the oxidationreduction reaction shown below. 4 points. What are the oxidation and reduction products for this reaction? 24As 2 S 3(s) + 80HNO 3(aq) + 32H 2 O (l) 9S 8(s) + 48H 3 AsO 4(aq) + 80NO (g) 8

9 33. Platinum can be precipitated out according to the reaction shown below. If a researcher wants 5.00 g PtBr 4 to form, but only wants to use 15.0 ml of hydrobromic acid, what molarity concentration does the acid need to be? Pt(NO 3 ) 4(aq) + 4HBr (aq) PtBr 4(s) + 4HNO 3(aq) 9

10 34. Identify aqueous solutions that, when mixed, will lead to formation of the indicated products. Reactants Product(s) H 2 O (l) PbI 2(s) H 2 O (l) + SO 2(g) 10

11 35. A 7.1 g sample of KCl was dissolved in enough water to make 49.1 g of solution. Before the addition of KCl, the initial temperature was C, and after the KCl dissolved, the temperature was C. Assuming no heat loss, calculate the H soln of KCl in kj/mole. Use C s = J/g C for the solution. 11

12 Answer Key for Exam A Section 1: Matching (10 points) (1) pascal (3) % yield (4) strong acid (2) q < 0 (6) state function (10) electrolyte (5) interhalogen compounds (7) hydronium (8) endothermic (9) P total = P 1 + P 2 + P P n CE. SI unit for pressure BE. exothermic AC. expresses efficiency of a reaction AD. an acid that completely ionizes in solution AB. covalent compounds between Group 17 elements CD. value does not depend on path AE. (H 2 O)H + or H 3 O + or H + BD. heat used as a reactant in a reaction DE. Dalton s Law of Partial Pressures BC. e.g. NaCl 1

13 Section 2: Multiple Choice (40 points)

14 Section 3: Long Answer (10 points each) 31. Answer: P Ne = atm and P Ar = atm. 32. Answer: Reactant side. As: + 3, S: 2, H: + 1, N: + 5, O: 2. Product side. S: 0, H: + 1, As: + 5, O: 2, N: + 2. Oxidation products: S 8(s) and H 3 AsO 4(aq). Reduction product: NO (g). 33. Answer: Need [HBr] = 2.59 M. 34. Answer: Many possible answers. Among them: HCl (aq) + NaOH (aq) ; Pb(NO 3 ) 2(aq) + NaI (aq) ; Na 2 SO 3(aq) + HCl (aq). 35. Answer: H soln = 23 kj/mole. 3