Midterm Previous Questions These questions were taken from previous midterm examinations from CHEM 120, which may be of assistance to you in studying. Please remember however that the course, and instructors, change from year to year, so many of these questions will not be as relevant to this year's CHEM 120 as some. This gives the impression of being more difficult than they were when given, since different homework was assigned, and more time may have been spent in class in some of these topics. Some terminology and variables may have changed somewhat too. Good luck studying. Solutions are also posted to WEB CT.
1. What is the work in joules done on the system to compress He gas from 24.0 L to 12.5 L against a pressure of 1.5 atm at a constant temperature of 37.4 C ? a. 5.5 103 b. 17 c. 17 d. 1.7 103 e. 1.7 103 2. 246 g of hot coffee at 86.0 C are placed in a 137 g mug at 20.0 C. The specific heat of coffee is 4.00 J/g C, while that of the mug is 0.752 J/g C. Assuming that no heat is lost to the surroundings, what is the final temperature of the system: mug + coffee? a. 79.7 C b. 93.7 C c. 98.4 C d. 76.0 C e. 53.0 C If the volume of a gas is doubled but the temperature remains constant, then: a. the pressure stays the same. b. the molecules move faster. c. the kinetic energy increases. d. the molecules move more slowly. e. none of these answers is correct. If we consider the Universe as one large thermodynamic system, we can say that over time : a. both the total Energy and the total Entropy are increasing. b. the total Energy is increasing and the total Entropy is decreasing. c. the total Energy is constant and the total Entropy is increasing. d. both the total Energy and the total Entropy are constant. e. the total Energy is decreasing and the total Entropy is increasing.
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5.
To increase the volume of a fixed amount of gas from 100 cm3 to 200 cm3, you could: a. increase the temperature from 25.0 C to 50.0 C at constant pressure. b. increase the pressure from 1.00 atm to 2.00 atm at constant temperature. c. reduce the temperature from 400 K to 200 K at constant pressure. d. reduce the pressure from 608 Torr to 0.40 atm at constant temperature. e. decrease the temperature from 600 K to 400 K.
2 NOCl(g) 2 NO(g) + Cl2(g) 2 NO2(g)
6.
H = H =
+75.56 kJ/mol
2 NO(g) + O2(g) 2 NO2(g)
H = -113.05
-58.03
N2O4(g)
Calculate the H of: N2O4(g) + Cl2(g) a. b. c. d. e. 7. +246.65 95.52 246.65 +95.52 none of these
2 NOCl(g) + O2(g) in kJ/mol.
What volume would be occupied by 4.8 g of oxygen gas at 0.50 atm and 133 C? a. 20 L b. 13 L c. 10 L d. 6.7 L e. 3.3 L If 356 J of work is done by a system while it loses 289 J of heat to the surroundings, what is the value of U? a. +645 J b. 645 J c. +67 J d. 67 J e. +134 J
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9.
The energy of molecules of a gas: a. is dependent on the concentration. b. is distributed over a wide range at constant temperature. c. is the same for all molecules at constant temperature. d. increases with a decrease in temperature. e. increases with an increase in pressure.
10.
The complete combustion of propane, C3H8(g), is represented by the equation:
C3H8(g) + 5 O2(g) 3 CO2(g) + 4 H2O(l)
H = -2220 kJ
How much heat is evolved in the complete combustion of 12.5 L C3H8(g) at 25 C and 790 Torr? a. 8.27 104 kJ b. 1.41 104 kJ c. 653 kJ d. 168 kJ e. 1180 kJ 11. The fossil fuel which burns with the greatest heat released (per gram) is also the fossil fuel which produces the least amount of carbon dioxide per kJ, and this is: a. coal. b. hydrogen. c. oil. d. natural gas. e. carbon dioxide.
12.
For the chemical bonds in usual molecules (such as methane gas), energy is released : a. when the bonds are formed. b. when the bonds are broken. c. when strong bonds are exchanged for weaker bonds. d. when weak bonds are exchanged for weaker bonds. e. both statements A) and C) are correct.
13. At 25.0C and 1.00 atm a gas sample occupies a volume of 1.50 L. At 100.0C and 1.00 atm, the same gas sample will occupy a. 0.375 L b. 1.20 L c. 1.88 L d. 6.00 L e. none of these 14. The average kinetic energy of the molecules in a gas depends on a. b. c. d. e. the temperature of the gas. the molecular mass of the gas molecules. the density of the gas. all of these none of these
15. How much heat energy is required to raise the temperature of 0.298 mole of water from 35.93C to 79.84C? a. 13.09 J b. 54.7 J c. 981 J d. 3310 J e. none of these
16. Given the following thermochemical equations, calculate the standard enthalpy of formation for propane, C3H8(g). C(s) + O2(g) CO2(g) H2(g) + O2(g) H2O(l) Hr = -393 kJ mol-1 Hr = -286 kJ mol-1 Hr = -2452 kJ mol-1
C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(l) a. b. c. d. e. -3131 kJ mol-1 129 kJ mol-1 4775 kJ mol-1 -1773 kJ mol-1 none of these
17. How much heat can be obtained from the complete combustion of 1.837 g of glucose to carbon dioxide and liquid water at constant pressure? Species glucose [C6H12O6(s)] CO2(g) H2O(l) a. b. c. d. e. 2800 kJ 595 kJ 28.56 kJ 6.067 kJ none of these Hf (kJ mol-1) -1274 -393 -286
18. The heat exchanged with the surroundings in a process carried out at constant pressure is a. w b. H c. CP / T d. E e. none of these
19. For a balloon expanding against atmospheric pressure, the work w done by the balloon is a. b. c. d. e. positive negative of indeterminate sign zero This cannot be answered without additional information.
20. A gas is compressed from 39.92 L to 12.97 L at a constant pressure of 5.00 atm. In the course of this compression 9.82 kJ of energy is released as heat. The work w for this process is a. 135 L atm b. -135 L atm c. -9.82 L atm d. 9.82 L atm e. This cannot be determined without additional information.
21. The enthalpy of vaporization of a substance is 23.35 kJ mol-1. Hence the enthalpy of freezing of this substance is a. -46.70 kJ mol-1 b. -23.35 kJ mol-1 c. 23.35 kJ mol-1 d. This cannot be determined from the available information. e. none of these Calculate the entropy change for methanol as it boils at 64.5 C. H = 38.0 kJ/mol. a. 0.589 kJ/molK b. 0.112 kJ/molK c. 589 kJ/molK d. 112 kJ/molK e. one must know G to calculate this
22.
23. If we consider the Universe as one large thermodynamic system, we can say that over time :
a. b. c. d. e. both the Energy total and the total Entropy are increasing. the total Energy is increasing and the total Entropy is decreasing. the total Energy is constant and the total Entropy is increasing. both the total Energy and the total Entropy are constant. the total Energy is decreasing and the total Entropy is increasing.
24.
Choose the INcorrect statement from the following: a. One form of the second law of thermodynamics states that all spontaneous processes produce an increase in the entropy of the universe. b. c. d. e. Gibbs free energy is defined by: G = H TS. If G < 0, the process is spontaneous. If G < 0, the reverse process is non-spontaneous. If G = 0, the process is spontaneous.
25.
Consider the following reaction:
C(g) + 2 H2(g) CH4(g) 186.19 J/mol-K
S 5.69
130.58
What is S for the above reaction in J/mol-K? a. b. c. d. e. 49.9 49.9 80.7 115.2 80.7
26.
A reaction is spontaneous if: I) G is a negative value. II) both enthalpy and entropy increase. III) H is negative and S is positive. IV) both enthalpy and entropy decrease. V) H is positive and S is negative. a. b. c. d. e. I and III I and II II and V III and IV this cannot be determined without knowing temperature
27.
Predict whether S is positive or negative for the following process:
2 Cl2O7(g) 2 Cl2(g) + 7 O2(g)
a. b. c. d. e.
negative. positive. there is not enough information to determine. S doesn't change. S changes the same on both sides of the equation.
28.
Which of the following combinations of signs for H and S will always result in a reaction being non-spontaneous? a. H+, S b. H, S+ c. H, Sd. H+, S+ e. one can not determine this without knowing the temperature.
29. Entropy is the thermodynamic property which constitutes a quantitative measure of the a. b. c. d. e. heat content of a system. degree of disorder of a system. internal energy of a system. all of these none of these
30. Which of the following processes should show the greatest increase in entropy? a. C6H6(l) + O2(g) 6CO2(g) + 3H2O(g) b. c. d. e. 2NO2(g) N2O4(g) C2H4(g) + H2(g) C2H6(g) BaS(s) + 2NaNO3(s) Ba(NO3)2(s) + Na2S(s) This cannot be predicted without additional information.
31. Consider the process whereby 1.00 mol of H2O(s) is melted to H2O(l) at the normal melting point of ice, 273.15 K. Which of the following is true for this process? a. H > 0 b. G = 0 c. H = TS d. All of these are true. e. None of these is true.
32. A reaction from unknown reactants (R): R P is spontaneous at 37 C and goes to completion. If the molar entropy of the products (P) is measured to be 460 J/molK, and 71.3 kJ of heat was given off in the process to the surroundings when 1 mol reacted, then the molar entropy of the reactants has to be: a. at most 690 J/molK b. at least 690 J/molK c. at most 230 J/molK d. at least 230 J/molK e. none of these
33. Consider the reaction, 2 SO2(g) + O2(g) 2 SO3(g), at T = 525C. This reaction has an equilibrium constant K = 781 at this temperature If = 0.400 atm, = 0.050 atm, and = 0.050 atm, the reaction a. b. c. d. e. will proceed by forming additional SO2(g) and O2(g). will proceed by forming additional SO3(g). is at equilibrium. The direction of the reaction cannot be predicted from these data. None of these is correct.
34)
A cubic room contains 4 gas molecules randomly distributed. The probability of observing exactly all of the molecules occupying just the left side of the room at any given time (creating `a vacuum' on the other side) is equal to: A) 1 chance in 4 B) 1 chance in 8 C) 1 chance in 16 D) 1 chance in 32 E) 2 chances in 32 35) For the thermal decomposition of calcium carbonate, the heat given off during the course of reaction is 178 kJ/mol, and the increase in entropy during the reaction is 161 J/molK. In order for the combustion of 2 mol of calcium carbonate to be spontaneous, the temperature needs to be: A) C) E) a maximum of 1106 K a maximum of 1.10 K a maximum of 2210 K B) a minimum of 1106 K D) a minimum of 1.10 K F) none of these answers is correct
36)
The solubility constant KS for calcium hydroxide is 5.5 x 106 . What is the highest pH that 0.1 mol/L of dissolved Ca(OH)2 can tolerate before being forced to precipitate as a solid? A) pH 11.9 C) pH 7.4 E) pH 2.1 B) pH 9.7 D) pH 4.3 F) none of these answers is correct
More Practice Questions for Chapter 6, supplied by Prof. Mittermaier. 1) Calculate the temperature at which the root-mean-square velocity of carbon dioxide (CO2) molecules is 500 m s-1. a) 714C b) 414C c) 441C d) 168C e) 1.62C 2) Calculate the height of a column of liquid glycerol (d = 1.26 g/cm3), in meters, required to exert the same pressure as 4.91 m of water. a) 3.65 m b) 5.16 m c) 4.91 m d) 6.19 m e) 3.90 m
3) A 4.00 L sample of N2(g) at 760 mmHg is compressed, at constant temperature, to 3.20 atm. What is the final gas volume? a) 950 L b) 0.771 L c) 1.25 L d) 13.1 L e) 59.6 L
4) 16) A sample of helium gas occupies a volume of 38 L at 780 torr and 25C. What volume would the gas occupy at standard temperature and pressure? a) 25 L b) 38 L c) 34 L d) 40 L e) 36 L
5) What volume would be occupied by 4.8 g of oxygen gas (O2) at 0.50 atm and 133C? a) 10 L b) 3.3 L c) 13 L d) 19 L e) 6.7 L 6) What is the density of carbon dioxide gas at -15C and 728 torr? a) 1512 g/L b) 2.08 g/L c) 1.84 g/L
d) 1.27 g/L e) 1.99 g/L 7) How many liters of H2 are needed to make 327 L of NH3 by the reaction: N2 (g) + 3 H2 (g) 2NH3 (g), if the gases are at the same temperature and pressure? a) 491 L b) 654 L c) 218 L d) 38.5 L e) 327 L
8) What is the volume, in L, occupied by a mixture of 16.0 g Ne(g) and 42.0 g Ar(g) at 15.0 atm pressure and 25 C? a) 94.6 L b) 1.29 L c) 3.01 L d) 0.252 L e) 1.71 L
9) In a gaseous mixture of neon and xenon that contains 50% neon by volume, a) the Ne and Xe atoms have the same average speed. b) there are more Ne atoms than Xe atoms. c) the Ne atoms are on the average moving more slowly than the Xe atoms. d) the total mass of Xe is equal to the total mass of Ne. e) the average kinetic energy of the Ne atoms is equal to that of the Xe atoms
10) A 40.2 L constant-volume cylinder containing 2.21 mol He is heated until the pressure reaches 4.20 atm. What is the final temperature? a) 658 K b) 931 K c) 804 K d) 1074 K e) 258 K