CHEM FINAL (test1)

11) The potential energy of a system of two atoms as a function of the internuclear distance is shown in the diagram above. Which of the following is true regarding the forces between the atoms when their internuclear distance is x? a. The attractive and repulsive forces are balanced, so the atoms will maintain an average internuclear distance x. b. There is a net repulsive force pushing the atoms apart, so the atoms will move further apart. c. There is a net attractive force pulling the atoms together, so the atoms will move closer together. d. It cannot be determined whether the forces between atoms are balanced, attractive, or repulsive, because the diagram show only the potential energy.

A

12) The synthesis of H2O(g) from O2(g) and H2(g) is represented by the equation above. Which of the following statements is true about bond energies in this reaction? a. The energy absorbed as the bonds in the reactants are broken is greater than the energy released as the bonds in the product are formed. b. The energy released as the bonds in the reactants are broken is greater than the energy absorbed as the bonds in the product are formed. c. The energy absorbed as the bonds in the reactants are broken is less than the energy released as the bonds in the product are formed. d. The energy released as the bonds in the reactants are broken is less than the energy absorbed as the bonds in the product are formed.

A

6) Based on the bond energies shown in the table above, which of the following diagrams best represented the change in energy as the reaction represented below proceeds?

A

9) A 10. g cube of copper at a temperature T1 is placed in an insulated cup containing 10. g of water at a temperature T2. If T1 > T2, which of the following is true of the system when it has attained thermal equilibrium? (The specific heat of copper is 0.385 J/(g C).) a. The temperature of the copper changed more than the temperature of the water. b. The temperature of the water changed more than the temperature of the copper. c. The temperature of the water and the copper changed by the same amount. d. The relative temperature changes of the copper and the water cannot be determined without knowing T1 and T2

A

10) The decomposition of H2O2(aq), represented by the equation below, is thermodynamically favorable. The signs of G and S for the reaction are which of the following? 2H2O2(aq) 2H2O(l) + O2(g) H = -196 kJ/molrxn G S a. Positive Positive b. Negative Positive c. Positive Negative d. Negative Negative

B

2) The potential energy as a function of internuclear distance for the three carbon-to-carbon bonds in ethane, ethene, and ethyne, is shown in the graph above. Based on the data in the graph, which of the following correctly identifies the carbon-to-carbon bonds as X, Y, and Z. X Y Z a. C2H6 C2H4 C2H2 b. C2H2 C2H4 C2H6 c. C2H4 C2H6 C2H6 d. C2H6 C2H6 C2H4

B

5) Which of the following is true for the combustion of C3H8 according to the data above. a. S > 0 and G > 0 b. S > 0 and G < 0 c. S < 0 and G < 0 d. S < 0 and G > 0

B

7) At 1.0 atm, a sample of water is cooled from liquid water and then to ice. The heating curve is shown in the graph above. Which of the following lists the signs for the changes in enthalpy and entropy for the process corresponding to segment X, going from right to left? H S a. Positive Negative b. Positive Positive c. Negative Negative d. Negative Positive

C

8) Which of the following equations represents a reaction for which the standard entropy change is positive (S > 0) a. 3 O2(g) 2 O3(g) b. 2 H2(g) + O2(g) 2 H2O (l) c. CaCO3(s) CaO(s) +CO2(g) d. I2(g) + 2 K(s) 2 KI(s)

C

A hot iron ball is dropped into a 200. g sample of water initially at 50°C. If 8.4 kJ of heat is transferred from the ball to the water, what is the final temperature of the water? (The specific heat of water is 4.2 J / (g °C) a. 40.C b. 51C c. 60.C d. 70.C

C

13) Based on the information above, what is the enthalpy change for the sublimation of iodine, represented below? I2(s) I2(g) a. 21 kJ / molrxn b. 31 kJ / molrxn c. 42 kJ / molrxn d. 62 kJ / molrxn

D

4) Calculate the standard heat of combustion for propane (C3H8). a. 500 b. 1900 c. -500 d. -1900

D

Questions 1 and 2 refer to the following molecules: ethane (C2H6), ethene (C2H4), and ethyne (C2H2). 1) Which of the following arranges the above molecules (C2H6, C2H4, and C2H2) in order of their carbon-to-carbon bond enthalpies from least to greatest. a. C2H2 < C2H4 < C2H6 b. C2H4 < C2H6 < C2H2 c. C2H6 < C2H2 < C2H4 d. C2H6 < C2H4 < C2H2

D