Please use the following constants and conversions in the problems below as needed Planck s constant: h = J-s Speed of Light:

Transcription

1 Please use the following constants and conversions in the problems below as needed Planck s constant: h = J-s Speed of Light: c = m/s Rydberg Constant: R H = m -1 Energy levels in hydrogen atom: E n = ( J)(1/n 2 ) 1. [7 points] Which one of the following is an exothermic process? (a) ice melting (b) water evaporating (c) boiling soup (d) condensation of water vapor (e) Ammonium thiocyanate and barium hydroxide are mixed at 25 C and the temperature drops 2. [7 points] The standard enthalpy of formation for ammonia, NH 3 (g), is H f = kj/mol. How much heat is released/absorbed when 1 mole of N 2 (g) is reacted with three moles of H 2 (g) to produce ammonia (at constant pressure)? (a) 46.2 kj of heat is released (b) 46.2 kj of heat is absorbed (c) 92.4 kj of heat is released (d) 92.4 kj of heat is absorbed (e) 23.1 kj of heat is released 3. [7 points] Consider the combustion reaction between octane and oxygen in the cylinder of an automobile. The reaction generates CO 2, H 2 O and heat, and at the same time the expanding gases push up the piston thereby powering the car. If the system is defined as the contents of the cylinder (not including the piston or the cylinder) which of the following statements is true for the system in this process? (a) The change in internal energy ( E) is negative (b) The change in internal energy ( E) is positive (c) The change in internal energy ( E) is zero (d) Not enough information is given to unambiguously determine the sign of E 4. [7 points] Which one of the following statements is true? (a) Enthalpy is an intensive property (b) The enthalphy change for a reaction does not depend upon the state (solid, liquid, gas, aqueous) of the reactants and products (c) Enthalpy is a state function (d) Enthalpy is equal to the heat measured under conditions of constant volume (e) If the enthalpy change of a reaction is H rxn the reverse reaction will have an enthalpy change equal 1/ H rxn

2 5. [7 points] Given the following standard enthalpies of formation: Br 2 (l) H f = 0 kj/mol Br 2 (g) H f = 30.7 kj/mol Br (g) H f = 112 kj/mol Which of the following statements is false? (a) Bromine is a liquid in it s standard state (b) The formation of Br 2 (g) from gas phase bromine atoms is endothermic (c) The evaporation (liquid gas) of bromine is endothermic (d) The condensation (gas liquid) of bromine is exothermic (e) Pick this answer if all of the above statements are true. 6. [7 points] If 25.0 g of sodium peroxide (Na 2 O 2, MW = 78.0 g/mol) is reacted with 12.1 g of water (H 2 O, MW = 18.0 g/mol) according to the following thermochemical equation: 2Na 2 O 2 (s) + 2H 2 O(l) 4NaOH(s) + O 2 (g) H = -126 kj What quantity of heat is released (assuming the pressure is held constant)? (a) kj (b) kj (c) kj (d) kj (e) -126 kj 7. [7 points] As an experiment you add a 155 g piece of aluminum (specific heat, C s = 0.90 J/g-K) and a 165 g piece of lead (specific heat, C s = 0.13 J/g-K) to a beaker of boiling water. After a few minutes both pieces of metal come to the same temperature as the water (100 C). Next you take both pieces of metal out of the water and set them on the benchtop. After 5 minutes you measure the temperature of each piece of metal. Assuming both pieces of metal lose heat at the same rate which of the following statements is true? (a) The lead will be cooler than the aluminum (b) The aluminum will be cooler than the lead (c) Both pieces of metal will be at the same temperature (d) There is not enough information given to know whether the lead or the aluminum will be cooler

3 8. [7 points] Given the following reactions Fe 2 O 3 (s) + 3CO (g) 2Fe (s) + 3CO 2 (g) 3Fe (s) + 4CO 2 (g) 4CO (g) + Fe 3 O 4 (s) H = kj H = kj What is H rxn for the following reaction? 3 Fe 2 O 3 (s) + CO (g) CO 2 (g) + 2 Fe 3 O 4 (s) (a) +109 kj (b) -109 kj (c) 15.5 kj (d) kj (e) -59 kj 9. [7 points] Given the following standard enthalpies of formation: Compound H f (kj/mol) PCl 3 (g) HCl(g) PH 3 (g) What is H for the following reaction: PCl 3 (g) + 3HCl(g) 3Cl 2 (g) + PH 3 (g) a. H rxn = kj b. H rxn = kj c. H rxn = kj d. H rxn = kj e. The H f of Cl 2 (g) is needed to complete the calculation. 10. [7 points] Acid-base neutralization reactions are typically exothermic. Because of this solutions can get quite hot when carrying out neutralization reactions. Given the following standard enthalpies of formation: Compound H f (kj/mol) Compound H f (kj/mol) HCl (aq) -167 H 2 O (l) -288 NaOH (aq) -470 NaCl (aq) -407 Calculate H for the following neutralization reaction: NaOH(aq) + HCl(aq) H 2 O(l) + NaCl(aq) (a) H rxn = +58 kj (b) H rxn = kj (c) H rxn = kj (d) H rxn = -58 kj (e) None of the above answers is correct.

4 11. [7 points] ml of 6.0 M sodium hydroxide solution is mixed with ml of 6.0 M hydrochloric acid solution in a calorimeter. What is the final temperature of the mixture if both solutions are at a temperature of 25.0 C before mixing? The density of the resulting solution is 1.02 g/ml and the specific heat is 4.18 J/g-K. Assume the calorimeter is perfect and no heat is lost to the surroundings. (a) 15.8 C (b) 83.0 C (c) 58.0 C (d) 40.8 C (e) 65.8 C 12. [7 points] The standard enthalpies of formation, H f, for CCl 4 (l) and CH 4 (g) are kj and kj respectively, and the heat of vaporization of carbon tetrachloride is endothermic by 32.6 kj/mol, as shown in the equation below: CCl 4 (l) CCl 4 (g) H rxn = kj Given this information calculate the enthalpy of the following reaction? (a) kj (b) 31.9 kj (c) 97.1 kj (d) kj (e) kj CH 4 (g) + 2Cl 2 (g) CCl 4 (g) + 2H 2 (g) 13. [7 points] What is the wavelength of light that has a frequency of 1.20 x Hz? (a) 25.0 m (b) m (c) m (d) 12.0 m (e) m 14. [7 points] What is the wavelength of a photon that has an energy of 5.25 x J? (a) m (b) m (c) m (d) m (e) 37,900,000 m

5 15. [7 points] Which of the following colors of light has the lowest energy photons? (a) green (b) violet (c) blue (d) red (e) yellow 16. [7 points] Einstein was able to explain the photoelectric effect by proposing that light behaves in some ways as a particle called a photon? For sodium metal it is known that only photons with energies equal to or greater than J are capable of ejecting electrons. Given this information which group of photons will be capable of ejecting one or more electrons from sodium? (a) Five photons each with an energy of J (b) Two photons each with a wavelength of 410 nm (c) Two photons each with a wavelength of 550 nm (d) Both (a) and (b) (e) All three (a), (b) and (c) 17. [7 points] Which of the following electronic transitions in a hydrogen atom lead to the emission of a photon with the shortest wavelength? (a) n=2 n=1 (b) n=3 n=2 (c) n=4 n=3 (d) n=5 n=4 (e) n=5 n=1 18. [7 points] The n = 2 to n = 6 transition in the Bohr hydrogen atom corresponds to the of a photon with a wavelength of. (a) emission, 411 nm (b) absorption, 411 nm (c) absorption, 657 nm (d) emission, 93.8 nm (e) emission, 389 nm 19. [7 points] According to the Heisenberg Uncertainty Principle, it is impossible to know precisely both the position and the of an electron. (a) mass (b) color (c) momentum (d) shape (e) wavelength

6 20. [7 points] Which quantum number defines the shape of an orbital? (a) principle, n (c) magnetic, m l (e) all orbitals have the same shape (b) azimuthal, l (d) spin, m s 21. [7 points] Which of the following electron configurations is correct for bromine? (a) [Ar] 4s 2 4p 5 (b) [Ar] 4s 2 4d 10 4p 5 (c) [Ar] 4s 2 3d 10 4p 5 (d) [Kr] 4s 2 4d 10 4p 5 (e) [Kr] 4s 2 3d 10 4p [7 points] How many unpaired electrons are there in a sulfur atom? (a) 1 (b) 2 (c) 3 (d) 4 (e) [7 points] How many electrons in a cadmium (Cd) atom have a magnetic quantum number, m l, equal to 2? (a) 0 (b) 2 (c) 4 (d) 10 (e) [7 points] Which of the following statements concerning nodes is false? (a) A node is where the electron wavefunction (ψ) changes sign (b) The probability of finding an electron at a node is zero (c) For a given orbital the number of nodal planes is equal to the azimuthal quantum number, l (d) All orbitals have at least one node (e) A 3p orbital has one radial node and one nodal plane 25. [7 points] Among the following sets of quantum numbers which set does not correspond to an electron in a zinc atom (in it s ground state)? (a) n = 4, l = 0, m l = 0, m s = +½ (b) n = 3, l = 0, m l = 0, m s = +½ (c) n = 3, l = 2, m l = -2, m s = -½ (d) n = 4, l = 2, m l = 2, m s = -½ (e) n = 2, l = 1, m l = -1, m s = -½