Unformatted text preview: Fall 2010 CH301 Practice Quiz 5—TA Style • QUESTION TYPE: Bomb calorimeter calculation When burned, ethanol (C2H5OH) has a H rxn of -1368 kJ mol 1 . Suppose that 43 grams of pure ethanol are burned in a bomb calorimeter containing 1 L of water. If the temperature increases by 50 C after the reaction occurs, what is the heat capacity of the calorimeter in J / C ? a. 5.7 J C 1 b. 23.2 J C 1 c. 121.7 J C d. 4152.6 J C 1 • QUESTION TYPE: Hess’ Law and calculating enthalpy changes Given the following data N 2 H 4 (l ) CH 4 O (l ) CH 2O ( g ) N 2 ( g ) 3H 2 g H 37 kJ N2H4 N2 l g H2 3H 2 g 2 NH 3 g 2NH 3 g g H 18 kJ H 46 kJ Calculate the enthalpy change of the following reaction. CH 4 Ol CH 2 O g H 2 g a. 65 kJ b. 65 kJ c. 101 kJ d. 101 kJ e. 27 kJ • QUESTION TYPE: Bond energy calculation The combustion of benzene in the presence of oxygen (O2) results in the production of CO2 and H2O. Write the balanced equation and determine the bond energy difference for this reaction. For this question use C=O bond energy of 799 kJ/mol, O=O bond energy of 498 kJ/mol, C‐H bond energy of 410 kJ/mol, O‐H bond energy of 498 kJ/mol, and ALL C‐C bonds (whether they are single or double bonds) as 481 kJ/mol. *Note: using a single bond energy value for C‐C single bonds and C‐C double bonds does not work in all cases. Benzene is a special case where this applies. a. ‐6990 kJ/mol b. 6990 kJ/mol c. 6.99 kJ/mol d. ‐6.99 kJ/mol • QUESTION TYPE: Work calculation 7 moles of a monatomic ideal gas are heated under constant external pressure and allowed to expand. The gas is heated from 240K to 340K. How much work is done by the gas? a. 5.8 kJ b. –5.8 kJ c. .058 kJ d. ‐.058 kJ • QUESTION TYPE: Sign convention Dr. Laude pours liquid nitrogen on a balloon filled with air. What can you say about the signs of heat, work, entropy change and free energy change as a student examines the result and exclaims, “yes, I can see liquid in the shrunken balloon!!”? a. ‐, ‐, ‐, ‐ b. ‐, +, +, ‐ c. ‐, ‐, ‐, + d. ‐, +, ‐, ‐ e. ‐, +, ‐, + f. +, ‐, +, ‐ g. ‐, +, +, ‐ h. ‐, +, +, + • QUESTION TYPE: Predicting entropy change Dissolved MgSO4 in water dissociates into its corresponding ions Mg2+ and SO42‐. Does the entropy increase or decrease and approximately how much more “disordered” is the system? a. Increase, four times more disordered b. Decrease, four times more disordered c. Increase, two times more disordered d. Decrease, two times more disordered • QUESTION TYPE: Temperature dependence of reaction spontaneity A reaction occurs spontaneously at 35 C but not at 200 °C . What are the signs of G , H , and S for this reaction at 35 C and 200 °C , respectively? 35 C 200 °C G H S G H S a. + + + + + + b. ‐ ‐ ‐ + + + c. ‐ ‐ ‐ + ‐ ‐ d. ‐ ‐ + + ‐ ‐ • QUESTION TYPE: Theory (laws, state functions, etc.) Consider the following statements. Which ones are true? I. Energy is conserved in an isolated system. II. Work and heat are state functions. III. The entropy of the system must increase for a reaction to happen. IV. The idea of an absolute zero temperature is associated with the third law. a. I and IV only b. II only c. III only d. I and II only e. II and III only f. I, II, and III The phrases “isolated system” and “universe” can be used interchangeably, and so the first statement is simply the first law of thermodynamics and is correct. Heat and work are path dependent and are the famous example of thermodynamics quantities that are NOT state functions (note they are not capitalized, q and w, like state functions are.) The second law states that the entropy of the universe must increase. It is possible for this to happen while either the system or surrounds have a net decrease in entropy. The third law defines an absolute zero for temperature and allows us to talk about what happens to matter as temperature of a system decreases. ...
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- Fall '10
- Digraph, 1 L, dr. laude, 5.7 J, g. ‐, h. ‐