CHE 11, Fall 1998
Test 2
November 2, 1998

Useful Information

1. Which of the following statements is not true? Oxidation and reduction

(a) cannot occur independently of each other.
(b) accompany all chemical changes.
(c) describe the loss and gain of electrons, respectively.
(d) result in a change in the oxidation states of the species involved.
(e) All are true.

2. Two metals of equal mass with different heat capacities are subjected to the same amount of heat. Which undergoes the smallest change in temperature?

(a) The metal with the higher heat capacity.
(b) The metal with the lower heat capacity.
(c) Both undergo the same change in temperature.
(d) You need to know the initial temperature of the metals.
(e) You need to know which metals you have.

3. Given the following two reactions at 298 K and 1 atm, which of the statements is true?

1. N_{2 (g)} + O_{2 (g)} 2 NO _(g) DH₁
2. NO _(g) + ½ O_{2 (g)} NO_{2 (g)} DH₂

(a) for NO_{2 (g)} is DH₂
(b) for NO _(g) is DH₁
(c) DH₁ = DH₂
(d) for NO_{2 (g)} = DH₂ + ½ DH₁

4. In Bohr’s atomic theory, when an electron moves from one energy level to another energy level more distant from the nucleus

(a) energy is emitted.
(b) energy is absorbed.
(c) no change in energy occurs.
(d) light is emitted.
(e) none of the above is true.

5. Which of the following does not have a standard enthalpy of formation equal to zero at 25 ^oC and 1.0 atm?

6. Which of the following statements about quantum theory is incorrect?

(a) The energy and position of an electron cannot be determined simultaneously.
(b) Lower energy orbitals are filled with electrons before higher energy orbitals.
(c) When filling orbitals of equal energy, two electrons will occupy the same orbital before filling a new orbital.
(d) No two electrons can have the same four quantum numbers.
(e) All of these statements are correct.

7. What distinguishes a strong acid from a weak acid? How can this property be experimentally determined? (7 points)

8. Write the net ionic equations for each of the following, referring to the solubility rules on the attached page. (8 points)

(a) AgNO_{3 (aq)} + BaCl_{2 (aq)}

(b) NiSO_{4 (aq)} + KOH _(aq)

9. In the hydrogen atom, what information do we get from the values of the quantum numbers, n, , and ? (9 points)

10. (a) How do the 2p orbitals differ from each other? (3 points)

(b) How do the 2p and 3p orbitals differ from each other? (3 points)

11. With what volume of 5.0 M HF will 7.4 g of calcium hydroxide react completely, according to the reaction shown below? (8 points)

2 HF + Ca(OH)₂ CaF₂ + 2 H₂O

12. A 3.31-g sample of lead nitrate is heated in an evacuated cylinder with a volume of 1.62 L. The salt decomposes when heated, according to the equation shown below.

2 Pb(NO₃)_{2 (s)} 2 PbO _(s) + 4 NO_{2 (g)} + O_{2 (g)}

Assuming complete decomposition of the lead nitrate, what is the total gas pressure inside the cylinder after decomposition and cooling to a temperature of 300 K? Assume the PbO (s) takes up negligible volume. (12 points)

13. At 25 ^oC, the following heats of reaction are known:

2 ClF + O₂ Cl₂O + F₂O D H = 167.4 kJ/mol
2 ClF₃ + 2 O₂ Cl₂O + 3 F₂O DH = 341.4 kJ/mol
2 F₂ + O₂ 2 F₂O D H = -43.4 kJ/mol

Calculate the DH for the reaction (at 25 ^oC). (10 points)

ClF + F₂ ClF₃

14. The heat of combustion for a sample of coal is 23.0 kJ/g. What quantity of this coal must be burned to heat 500. g of water from 20.0 ^oC to 90.0 ^oC? The heat capacity of water is . (8 points)

15. When an electron in a 2p orbital of a lithium atom makes a transition to the 2s orbital, a photon of wavelength 670.8 nm is emitted. Calculate the energy difference between these orbitals. (5 points)

Essay. Write your answer in complete sentences, using proper grammar. (15 points)

16. What are the basic assumptions of the kinetic-molecular theory? Which of these assumptions are most nearly correct and which are violated to some extent by a real gas?