Please use the following constants and conversions in the problems below as needed h = J-s

Transcription

1 Please use the following constants and conversions in the problems below as needed h = J-s R H = m c = m/s Avogadro s Number = [7 points] Which of the following statements regarding enthalpy is false? (a) Enthalpy is a state function (b) Enthalpy is an extensive property (c) To determine the enthalpy of a reaction it is necessary to know the mechanism by which the reaction proceeds. (d) The enthalpy of a reaction is equal to the heat produced/absorbed by the reaction when it occurs at constant pressure (e) The enthalpy change for a reaction depends upon the state (solid, liquid, gaseous or aqueous) of the products and reactants 2. [7 points] Which of the following equations represents the standard enthalpy of formation of ammonium chloride? (a) N 2 (g) + H 2 (g) + Cl 2 (g) NH 4 Cl(s) (b) N 2 (g) + 4H 2 (g) + Cl 2 (g) 2NH 4 Cl(s) (c) N(g) + 2H 2 (g) + Cl(g) NH 4 Cl(s) (d) ½N 2 (g) + 2H 2 (g) + ½Cl 2 (g) NH 4 Cl(s) (e) N (g) + 4H(g) + Cl(g) NH 4 Cl(s) 3. [7 points] Which of the following processes are endothermic? (a) Freezing water (liquid solid) (b) Boiling water (liquid gas) (c) The combustion of methane [CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(g)] (d) Electrolysis of water [2H 2 O(l) 2H 2 (g) + O 2 (g)] (e) Both (b) and (d) are endothermic. 4. [7 points] There are two forms of elemental phosphorous, white phosphorous, which has a standard enthalpy of formation, H f = 0 kj/mol, and red phosphorous, which has a standard enthalpy of formation, H f = kj/mol. Given this information which of the following statements is true? (a) White phosphorous is more stable than red phosphorous (b) Red phosphorous is more stable than white phosphorous (c) Conversion of red phosphorous to white phosphorous will generate heat (d) Both (a) and (c) are true statements. (e) Both (b) and (c) are true statements.

2 5. [7 points] If g of methanol (CH 3 OH, MW = 32.0 g/mol) is reacted with 12.1 g of oxygen (O 2, MW = 32.0 g/mol) according to the following thermochemical equation: 2CH 3 OH (l) + 3O 2 (g) 2CO 2 (g) + 4H 2 O(l) H = kj What quantity of heat is released (assuming the pressure is held constant)? (a) -183 kj (b) -258 kj (c) -547 kj (d) -516 kj (e) kj 6. [7 points] As an experiment you add a piece of aluminum (specific heat, C s = 0.90 J/g-K) that has been heated to 90 C to a constant pressure calorimeter containing 55 g of water at 25 C. After the system has come to equilibrium you measure the final temperature of the mixture. Now you repeat the experiment keeping all variables the same except that you replace the aluminum with a piece of iron (specific heat, C s = 0.45 J/g-K) of identical mass (also at 90 C). Which of the following statements is true? (a) The calorimeter containing the aluminum will attain a higher final temperature (b) The calorimeter containing the iron will attain a higher final temperature (c) Both calorimeters will attain the same final temperature (d) There is not enough information given to know which calorimeter will have a higher final temperature 7. [7 points] Given the following thermochemical equations: 4B(s) + 3O 2 (g) 2B 2 O 3 (s) 2H 2 (g) + O 2 (g) 2H 2 O(l) B 2 H 6 (g) + 3O 2 (g) B 2 O 3 (s) + 3H 2 O(l) H = kj H = -572 kj H = kj Use Hess law to calculate the standard enthalpy of formation of diborane, B 2 H 6 (g): (a) 4260 kj (b) kj (c) 933 kj (d) kj (e) None of the above

3 8. [7 points] A ml sample of 2.0 M sodium hydroxide solution at 25.0 C is mixed with ml of 6.0 M sulfuric acid solution also at 25.0 C in a calorimeter. 2 NaOH(aq) + H 2 SO 4 (aq) 2 H 2 O(l) + Na 2 SO 4 (aq) After the reaction occurs the temperature of the resulting mixture is measured to be 38.5 C. The density of the resulting solution is 1.02 g/ml and the specific heat is 4.18 J/g-K. What is H for this reaction (sodium hydroxide is the limiting reactant)? Assume no heat loss to the surroundings. (a) H rxn = -48 kj (b) H rxn = -96 kj (c) H rxn = -24 kj (d) H rxn = +96 kj (e) None of the above answers is correct. 9. [7 points] Given the following standard enthalpies of formation: Compound H f (kj/mol) CH 4 (g) -75 CO 2 (g) -394 H 2 O(g) -242 What is the standard enthalpy change for the combustion of methane: CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(g) (a) +561 kj (b) 561 kj (c) +803 kj (d) 803 kj (e) 711 kj 10. [7 points] Which of the following processes does not involve a conversion to or from chemical energy. (a) Discharging the battery in a cell phone (b) Driving a gasoline powered automobile (c) Photosynthesis (d) Generating electricity at a hydroelectric power plant (e) Generating electricity at a coal fired power plant

4 11. [7 points] A He-Ne laser emits light with a wavelength of 655 nm. What is the frequency of this radiation? (a) 197 Hz (b) Hz (c) Hz (d) Hz (e) Hz 12. [7 points] What is the energy of the photons emitted from the He-Ne laser in problem 11? (a) J (b) J (c) J (d) J (e) J 13. [7 points] Which of the following types electromagnetic radiation has the lowest energy photons? (a) visible light (b) microwaves (c) infrared (d) ultraviolet (e) x-rays 14. [7 points] Which of the following electronic transitions in a hydrogen atom lead to the emission of photons in the visible region of the spectrum? (a) n=2 n=1 (b) n=3 n=2 (c) n=4 n=3 (d) n=5 n=4 (e) n=5 n=3 15. [7 points] Which of the following statements is not consistent with the Bohr model of the hydrogen atom? (a) The energy of an electron increases (becomes less tightly bound to the nucleus) as the principle quantum number increases. (b) The electron energy levels are quantized. (c) The electron is considered to be both a particle and a wave. (d) The electrons orbit the nucleus in well defined spherical orbits. (e) The radius of the electron orbit increases as the principle quantum number increases.

5 16. [7 points] A strip of sodium metal is bombarded by violet light (wavelength = 410 nm) at a rate of 10,000 photons per second, which causes a steady stream of electrons to be ejected from the metal, via the photoelectric effect. The minimum energy required to eject an electron from sodium is J. What will happen if the sodium is now bombarded by red light (wavelength = 700 nm) at a rate of 10,000 photons/second? (a) The number of electrons ejected per second will decrease (b) The number of electrons ejected per second will increase (c) Electrons will no longer be ejected (d) The rate of ejected electrons will remain constant, but the kinetic energy of the ejected electrons will decrease (e) The rate of ejected electrons will remain constant, but the kinetic energy of the ejected electrons will increase 17. [7 points] Which of the following electron configurations is correct for mercury (Hg)? (a) [Kr] 6s 2 6f 14 6d 10 (b) [Xe] 4s 2 5f 14 6d 10 (c) [Xe] 6s 2 4f 14 6d 10 (d) [Xe] 6s 2 5d 10 (e) [Xe] 6s 2 4f 14 5d [7 points] How many electrons in a gallium atom (Ga) have an azimuthal quantum number, l, equal to 2? (a) 15 (b) 5 (c) 8 (d) 10 (e) [7 points] Consider an electron residing in a 5p orbital in an atom of bismuth. Which of the following statements is false? (a) The electron has an azimuthal quantum number of l = 1 (b) The electron is higher in energy than the electrons in the 4d orbitals (c) The electron wavefunction has one nodal plane (d) The value of its magnetic quantum number, m l, may be 1 (e) The electron is higher in energy than the electrons in the 4f orbitals

6 20. [7 points] For the following elements: Gd, Ga, Pu & K, identify the highest energy occupied subshell (the type of orbital in which the highest energy electron resides in). (a) Gd 6f Ga 4p Pu 7f K 4s (b) Gd 4f Ga 4s Pu 5f K 4p (c) Gd 4f Ga 4p Pu 5f K 4s (d) Gd 3f Ga 4p Pu 4f K 4s (e) Gd 1f Ga 3p Pu 2f K 4s 21. [7 points] Which of the following statements is false? (a) The energy level of an orbital in a multielectron atom depends upon the value of the principle (n) and azimuthal (l) quantum numbers (b) The wavefunction, ψ, changes sign at each node (c) The wavefunction for a 1s orbital doesn t have any nodes (d) The wavefunction for a 2p z orbital has two nodal planes (e) The probability density, ψ 2, goes to zero at each node 22. [7 points] As we move down group 15 of the periodic table (N Bi) which one of the following statements is false? (a) The number of unpaired electrons remains the same (b) The atomic radius increases (c) The 1 st ionization energy increases (d) The size of the 2s orbital decreases 23. [7 points] Which of the following elements has the highest 4 th ionization energy? (a) Te (b) Se (c) As (d) In (e) Ge 24. [7 points] Which of the following elements has the highest 1 st ionization energy? (a) Cl (b) I (c) Se (d) S (e) Na 25. [7 points] Arrange the following elements: Ne, Cl, Se, Br & Sb, in order of increasing atomic radius. (a) [smallest] Ne < Se < Cl < Br < Sb [largest] (b) [smallest] Sb < Se < Br < Cl < Ne [largest] (c) [smallest] Ne < Br < Cl < Se < Sb [largest] (d) [smallest] Ne < Cl < Br < Se < Sb [largest] (e) [smallest] Cl < Br < Se < Sb < Ne [largest]