CPC CPC Physical Chemistry & Thermodynamics 2 — Questions and Answers
Question 1: The Clausius-Clapeyron equation describes the relationship between vapor pressure and:
- Molar mass and boiling point
- Temperature and enthalpy of vaporization (Correct answer)
- Surface tension and viscosity
- Density and molecular weight
Correct answer: Temperature and enthalpy of vaporization
The Clausius-Clapeyron equation ln(P2/P1) = −ΔHvap/R × (1/T2 − 1/T1) relates vapor pressure changes to temperature and the molar enthalpy of vaporization.
Question 2: Which quantum number determines the shape of an atomic orbital?
- Principal quantum number (n)
- Angular momentum quantum number (l) (Correct answer)
- Magnetic quantum number (ml)
- Spin quantum number (ms)
Correct answer: Angular momentum quantum number (l)
The angular momentum quantum number l defines the orbital shape: l=0 (s, spherical), l=1 (p, dumbbell), l=2 (d, more complex).
Question 3: For a reaction at equilibrium, doubling the concentration of a reactant that appears as first order will change the reaction quotient Q by a factor of:
- 0.5
- 1 (no change)
- 2 (Correct answer)
- 4
Correct answer: 2
If a reactant appears as first order in the rate expression, doubling its concentration multiplies Q by 2, shifting the reaction toward products if Q > K.
Question 4: The Born-Haber cycle is used to calculate the lattice energy of an ionic compound by applying:
- Hess's law to a series of enthalpy steps (Correct answer)
- The van't Hoff equation to ionic solutions
- The Nernst equation to electrochemical cells
- Graham's law to ion diffusion
Correct answer: Hess's law to a series of enthalpy steps
The Born-Haber cycle applies Hess's law, summing experimentally known enthalpies (sublimation, ionization, electron affinity, dissociation, formation) to determine the otherwise inaccessible lattice energy.
Question 5: Which spectroscopic technique measures the absorption of microwave radiation to give information about molecular bond lengths and angles?
- NMR spectroscopy
- Rotational (microwave) spectroscopy (Correct answer)
- IR spectroscopy
- UV-Vis spectroscopy
Correct answer: Rotational (microwave) spectroscopy
Microwave (rotational) spectroscopy probes transitions between rotational energy levels, providing precise molecular geometry data including bond lengths and bond angles.
Question 6: According to the Henderson-Hasselbalch equation, a buffer has maximum buffering capacity when:
- pH = 2 × pKa
- pH = pKa (Correct answer)
- pH = pKa + 2
- pH = pKb
Correct answer: pH = pKa
When pH = pKa, the concentrations of weak acid and conjugate base are equal, maximizing the buffer's ability to neutralize both added acid and base.
CPC CPC Physical Chemistry & Thermodynamics 2
The Clausius-Clapeyron equation describes the relationship between vapor pressure and: