CHE 101 Exam 2 Notes

Section 1: Multiple Choice Questions

  • Question 1: A system releases 365 kJ of heat and does 729 kJ of work. What is the change in internal energy?

    • Answer: c. −364 kJ
    • Calculation:
    • Change in internal energy (ΔU) is given by the formula:

      ext{ΔU} = q + W

      where:
    • q = heat exchanged (negative for heat released) = -365 kJ
    • W = work done by system (positive) = -729 kJ
    • Thus,

      ext{ΔU} = -365 kJ - 729 kJ = -1094 kJ
    • Common misconception: This is due to misunderstanding signs in thermodynamic formulas.

  • Question 2: Which of the following is not an accurate expression of the First Law of Thermodynamics?

    • Answer: b. Energy cannot be converted between forms.
    • Explanation: The First Law states that energy can be transformed from one form to another.

  • Question 3: Which of the following reactions and processes is exothermic?

    • Answer: a. Freezing of water: H2O (l) → H2O (s)
    • Explanation: Exothermic processes release heat, such as phase changes from liquid to solid.

  • Question 4: Which of the following is not a property of ideal gases?

    • Answer: d. They have physical properties that vary greatly with composition.
    • Ideal gases are characterized by uniform behaviors regardless of the composition of the gas.

  • Question 5: A 2.50 L container contains 0.500 moles of an ideal gas at a pressure of 5.00 atm. What is the temperature of the gas in Kelvin?

    • Answer: b. 305 K
    • Use Ideal Gas Law:
      PV = nRT

      where R = 0.0821 L·atm·K⁻¹·mol⁻¹.

  • Question 6: What is the partial pressure of O2 in the atmosphere if the mole fraction is 0.2095 and atmospheric pressure is 760 torr?

    • Answer: c. 159 torr
    • Calculation:

      P_{ ext{O2}} = (0.2095)(760 ext{ torr}) = 159.22 ext{ torr}

  • Question 7: Graph depicting how the volume of a fixed amount of an ideal gas depends on temperature at constant pressure?

    • The graph should be linear since volume and temperature are directly proportional (Gay-Lussac's Law).

  • Question 8: Moles of gas at pressure of 2280 torr, temperature of -118 °C, volume of 2.00 L?

    • Use Ideal Gas Law.
    • Answer: b. 0.620 moles
    • Conversion needed for temperature: extT(K)=−118+273.15=155.15extKext{T(K)} = -118 + 273.15 = 155.15 ext{ K}

  • Question 9: Valid set of quantum numbers?

    • Answer: e. n = 2, l = 1, ml = -1, ms = 1/2

  • Question 10: Experimental measurements from the photoelectric effect?

    • Answer: c. Particle-like behavior of light

  • Question 11: Which transition absorbs the lowest energy photon?

    • Answer: c. n = 6 → n = 5
    • Explanation: The energy difference between states determines absorbed photon energy.

  • Question 12: Number of atomic orbitals with principal quantum number n = 2?

    • Answer: b. 2
    • Explanation: 2s and 2p orbitals exist.

  • Question 13: Effect of light frequency increase?

    • Answer: a. the energy of the light increases
    • Explanation: Energy is related to frequency by E=h<br/>νE = h<br />\nu.

  • Question 14: Values of angular momentum quantum numbers for given orbitals?

    • Answer: c. Orbital #1: l = 1, Orbital #2: l = 2

Section 2: Full Answer Questions

  • Question 15: Enthalpy change for reaction: 2C(s) + O2(g) → 2CO(g):

    • Given equations:
    • C(s)+O2(g)→CO2(g)ext,where∆H=−393.7extkJC(s) + O2(g) → CO2(g) ext{, where } ∆H = -393.7 ext{ kJ}
    • 2CO(g)+O2(g)→2CO2(g)ext,where∆H=−566.6extkJ2CO(g) + O2(g) → 2CO2(g) ext{, where } ∆H = -566.6 ext{ kJ}
    • Determine:
    • Combine above reactions to form desired reaction and calculate ΔH.

  • Question 16: Standard molar enthalpy of formation for ethylene (C2H4):

    • Given:
    • C2H4(g)+3O2(g)→2CO2(g)+2H2O(g)ext,where∆H°=−1323.1extkJ/molC2H4(g) + 3O2(g) → 2CO2(g) + 2H2O(g) ext{, where } ∆H° = -1323.1 ext{ kJ/mol}
    • Calculate using intermediate products’ enthalpies.

  • Question 17: Calculate the enthalpy change (∆H) for a reaction causing a temperature increase of 18.5 °C in a 125 g solution with specific heat capacity 4.184 J/(g °C):

    • ext∆H=mimesCsimesΔT=125extgimes4.184extJ/(g°C)imes18.5°Cext{∆H} = m imes Cs imes ΔT = 125 ext{ g} imes 4.184 ext{ J/(g °C)} imes 18.5 °C

  • Question 18: Enthalpy change for the decomposition of 285.9 kg of CaCO3:

    • Given: extCaCO3(s)→extCaO(s)+extCO2(g),∆H=178.3extkJext{CaCO3(s)} → ext{CaO(s)} + ext{CO2(g)}, ∆H = 178.3 ext{ kJ}

  • Question 19: Calculate mass of CO2 consumed in photosynthesis with 3854 kJ absorbed:

    • Given: 6CO2(g)+6H2O(l)→C6H12O6(s)+6O2(g),∆H=2801kJ6CO2(g) + 6H2O(l) → C6H12O6(s) + 6O2(g), ∆H = 2801 kJ

  • Question 20: Enthalpy change calculation using given reactions for reaction: HCN(g)+3H2(g)→CH4(g)+NH3(g)HCN(g) + 3H2(g) → CH4(g) + NH3(g)

  • Question 21: Calculate mass of helium gas in a balloon:

    • Given conditions: 15.0 L, 302 K, 1.00 atm; utilize ideal gas calculations.

  • Question 22: Final partial pressures for mixed gases after valve is opened:

    • Initial pressures need to be adjusted based on total volume.

  • Question 23: New pressure after temperature change at constant volume:

    • Use the formula P1/T1=P2/T2P1/T1 = P2/T2 to find new pressure.

  • Question 24: Balloon volume change as it ascends to altitude with new pressure and temperature.

  • Question 25: Find the wavelength corresponding to photon energy: Ephoton=1.39imes10−19extJE_{photon} = 1.39 imes 10^{-19} ext{ J}.

  • Question 26: Calculate de Broglie wavelength of an electron: λ=hmvλ = \frac{h}{mv}.

  • Question 27: Complete the subshell table with missing quantum numbers and subshell names.

  • Question 28: Sketch contour representation for 1s and 2py orbitals.

  • Question 29: Draw orbital diagram for manganese (Mn), indicating occupancy of orbitals.

  • Question 30: Write ground state electron configurations for Na, F, Mn, and Pb.