Chemistry 3202 Unit Test : Thermochemistry Name:_ Part A: Multiple Choice. Circle the best answer for each question. Answer all questions in this section. (24 pts) 1. A heated 250 g sample of aluminium metal is placed in water at room temperature. The water absorbs 264 J of heat from the metal and increases in temperature to 34.9 O C. What was the initial temperature of the aluminium? ( cal = 0.900 J/g O C) a. 11.7 O C b. 23.2 O C c. 36.1 O C d. 46.6 O C 2. Given in the thermochemical equation below, what is the molar enthalpy of formation for N2O? 2N2O(g) 2N2(g) + O2(g) + 163.3 kj a. -163.3 KJ/mol b. -81.6 KJ/mol c. 81.6 KJ/mol d. 163.3 KJ/mol 3. Which of the following is has an enthalpy of formation of 0 KJ/mol? a. N 2 (g) b. Hg (s) c. N 2 (s) d. N 2 (l) 4. A piece of ice was dropped into liquid water to determine the molar heat of fusion of water. What is the best interpretation of the results as shown in the graph below? a. The ice finishes melting at 2 minutes and heat enters the container b. The ice finishes melting at 2 minutes and heat leaves the container c. The ice finishes melting at 5 minutes and heat enters the container d. The ice finishes melting at 5 minutes and heat leaves the container.
5. What is the symbol for the enthalpy change when a substance changes from a solid to a liquid, under standard conditions? ANS: B 6. Which is the correct order of energy changes from greatest to least? a. Chemical Nuclear Physical b. Chemical Physical Nuclear c. Nuclear Chemical Physical d. Nuclear Physical Chemical 7. What is the melting point of the substance in the graph below, in degrees celsius? a. 30 b. 60 c. 100 d. 120 8. Which bond energy would be most precisely known? a. C-Cl b. O-H c. C=O d. H-F 9. A leaky thermos would be an example of a(n): a. Open System b. Closed System c. Insulated System d. Isolated System
10. 11. What is the fuel value of a 3.00 g sample of banana that produces 12 110 J of energy? a. 2.48 KJ/g b. 4.04 KJ/g c. 16.2 KJ/g d. 36.3 KJ/g 12. Given the reaction below: ANS: B C6H6(l) 3C2H2(g) H rxn = 632 kj and the H f of C6H6(l) = 49 kj/mol, what is H f of C2H2(g)? Part B: (26 pts) Answer all questions: a. -681 KJ/mol b. -227 KJ/mol c. 227 KJ/mol d. 681 KJ/mol 13. a.(3pts) A new bomb calorimeter is purchased by Mealy Mountain Collegiate. It is first calibrated by combusting 1.55g of Ethanol (C 2 H 5 OH) (Enthalpy of Combustion = -1368 KJ/mol) and a temperature change of 4.001 O C is observed. Determine the Heat Capacity of the bomb calorimeter. ANS: C= 11.5 KJ/ O C
b. 3pts. After calibration of the bomb calorimeter, a 0.200 mol sample of another alcohol was combusted in excess oxygen, and the recorded temperature change was 13.10 O C. What is the enthalpy of combustion of the other alcohol? ANS: Enthalpy of Combustion = -753 KJ/mol c. 2pts Based on your answer in b), and the data given in a), what alcohol do you think was combusted in b)? Why? (Methanol, smaller molecule than Ethanol, so lower Enthalpy of Combustion 14. Use the following equations to find the enthalpy change of the formation of methane, CH4, from chloroform, CHCl3. (6pts) CHCl3(l) + 3 HCl(g) CH4(g) + 3Cl2(g) (1) ½ H 2(g) + ½ Cl 2(g) HCl (g) H O = -92.3 kj (2) C (s) + 2H 2(g) CH 4(g) H O = -74.8 kj (3) C (s) + ½ H 2(g) + 3/2Cl 2(g) CHCl 3(l) H O = -134.5 kj H O = 336.6 KJ
15. a. 4pts. Calculate the total energy required to heat a 40.0g sample of ice from -35 O C to 40 O C (c ice = 2.01 j/g O C) ANS: 22.9 KJ b. 2 pts. Draw a heating curve for the process in a).
16. 6pts ANS: -2034 KJ/mol BONUS: Points will only be awarded for a correct numerical value*** (3pts) A 25.0g sample of a mysterious substance (145.0g/mol) is heated from 80.5 O C to 146.5 O C and melts at some point during the process. H O fus= 400.0 kj/mol. If a total energy change of 82.0 kj is observed, determine the melting point. (c solid = 5.44 j/g O C, c liquid = 7.22 j/g O C)