1. During a hot day a section of railroad track is observed to increase temperature from 50° to 110°C. The section of track is made of iron, and has a mass of 233 x 10³ moles. If the specific heat of iron is 0.45 J g^-1 K^-1, how much heat energy was absorbed by the section of track? (5 points)

DT = 110-50 = 60°C (60K)

mass: 233 x 10³ moles * (55.8g/mole) = 13.0 x 10⁶ g (13,000 kg)

heat transferred = specific heat * grams of substance * DT

heat transferred = 0.45 J g^-1 K^-1 * 13.0 x 10⁶ g * 60K

heat transferred = 351 x 10⁶ J

Note: 2 points for specific heat equation, 3 points for correct energy

2. 50 mls of an aqueous solution of NaOH and 100 mls of an aqueous solution of HCl are combined and allowed to react in a constant pressure calorimeter. The reaction generated 2.51 kJ of heat energy. Assuming the specific heat of water is 4.18 J g^-1 K^-1 and the density of water is 1.0g/ml, what will be the temperature change of the solution? (5 points)

DT = quantity of heat transferred/(grams of substance * specific heat)

DT = 2.51 x 10³ J/(150 mls * 1g/ml * 4.18 J g^-1 K^-1)

DT = 4K

Note: 2 points for specific heat equation, 3 points for correct DT

3. Given the following information:

C(s) + 2H₂(g) + 1/2O₂(g) -> CH₃OH(l) DH = -239 kJ

C(s) + O₂(g) -> CO₂(g) DH = -394 kJ

H₂(g) + 1/2O₂(g) -> H₂O(l) DH = -286 kJ

Calculate DH for the combustion of 15 grams of methanol (10 points)

2CH₃OH(l) + 3O₂(g) -> 2CO₂(g) + 4H₂O(l)

2C(s) + 2O₂(g) -> 2CO₂(g) DH = -788 kJ

4H₂(g) + 2O₂(g) -> 4H₂O(l) DH = -1144 kJ

2CH₃OH(l) -> 2C(s) + 4H₂(g) + O₂(g) DH = 478 kJ

2CH₃OH(l) + 3O₂(g) -> 2CO₂(g) + 4H₂O(l) DH = -1454 kJ

(-1454 kJ/2 moles CH₃OH) * (15 g CH₃OH) * (1 mole/32.0g) = -341 kJ

3 points balanced equation, 5 points correct combustion DH, 2 points for gram calculation

4. From the information and results in question #3 draw an enthalpy diagram which shows the formation of CH₃OH(l), CO₂(g) and H₂O(l) from elemental forms, and which also shows the enthalpy associated with the combustion of CH₃OH(l) to form CO₂(g) and H₂O(l) (10 points)



5. An electron transitions from the n=4 to the n=1 principle quantum number in the hydrogen atom. Is energy emitted or absorbed for the associated electron transition? What is the wavelength of the associated photon? Is this photon visible, and if not, what part of the electromagnetic spectrum is the wavelength located? (5 points)

Freq=(R_H /h)*(1/n_i² – 1/n_f²) = (2.18 x 10^-18 J/6.63 x 10^-34 J s)*(1/16 – 1/1) = -3.08x10¹⁵s^-1

Energy is EMITTED

Wavelength = c/freq = (3x10⁸ m/s)/(-3.08x10¹⁵s^-) = 9.73 x 10^-8, or 97.3 nm

This is outside the visible spectrum, and is located in the ultraviolet spectrum.

1 point for Rydberg equation, 1 points for emission, 2 points for correct wavelength, 1 point for visibility

6. List the various subshells, and the number of orbitals in each subshell, for the shell with a principle quantum number of 3. How many total orbitals are there? (5 points)

n=3 , l = 0,1,2, (s, p, d)

3s 1 orbital

3p 3 orbitals

3d 5 orbitals

9 orbitals total

1 point each orbital name, 2 points for correct # of orbitals

7. What is the effective nuclear charge on the 4s valence electrons of Calcium? (5 points)

Calcium is [1s² 2s² 2p⁶ 3s² 3p⁶] 4s², with Z = 20

Zeff = 20-18 = 2+

 

8. What elements are represented by the following electron configurations? (10 points)

1s² 2s² 2p⁴ O

[Ne] 3s² Mg

1s² 2s² 2p⁶ 3s² 3p⁶ Ar

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁴ Se

[Ar] 4s¹ 3d¹⁰ Cu

9. Write orbital diagrams for the following elements (10 points)

Fe



C



 

10. How does the effective nuclear charge change as you move from right to left across the periodic table? How does the effective nuclear charge change as you move up a group in the periodic table? (5 points)

Z_eff decreases as you move from right to left

Z_eff unchanged as you move up

 

11. Of the Noble gas elements Ne, Ar and Kr, which one would have its n=2 orbital shell closest to the nucleus? (5 points)

Kr

 

 

12. Which element, or ion, below has the lowest ionization energy? (5 points)

Na⁺ Cl^- O^2- Mg²⁺ Li

13. Given the following information, determine the bond length for diatomic Oxygen (5 points)

C-O 1.43Å

C-C 1.54Å

C-N 1.43Å

N-N 1.47Å

14. For the following pairs of elements indicate which one most likely has a more negative (i.e. greater) electron affinity (5 points)

Li Be

S Cl

F Ne

Mg Al

Ar K

15. Name five characteristics of metals (5 points)

a) Have a shiny luster

b) Malleable and ductile

c) Conductors of heat and electricity

d) Oxides are ionic solids that are basic

e) Tend to form cations in aqueous solution

16. Write the expected balanced equations for the following reactions involving metals (be sure to include the states of the reactants and products): (5 points)

a) Magnesium oxide plus water

b) Calcium oxide plus a dilute solution of hydrochloric acid