Chemistry Test Physical Chemistry 3 ā Questions and Answers
Question 1: Which of the following best describes the Maxwell-Boltzmann distribution for an ideal gas at higher temperature?
- Narrower and taller peak shifted to lower speeds
- Broader and shorter peak shifted to higher speeds (Correct answer)
- Unchanged shape at any temperature
- Narrower and taller peak shifted to higher speeds
Correct answer: Broader and shorter peak shifted to higher speeds
Higher temperature increases average molecular speed and broadens the distribution, resulting in a lower, wider curve shifted toward higher speeds.
Question 2: The critical point of a substance is defined as the temperature and pressure above which:
- Only the solid phase exists
- Liquid and gas phases become indistinguishable (Correct answer)
- The substance decomposes
- Only the gas phase exists
Correct answer: Liquid and gas phases become indistinguishable
Above the critical point, distinct liquid and gas phases cease to exist, and the substance exists as a supercritical fluid.
Question 3: Henry's Law states that the solubility of a gas in a liquid is:
- Inversely proportional to pressure
- Independent of temperature
- Directly proportional to partial pressure of the gas (Correct answer)
- Equal to the vapor pressure of the solvent
Correct answer: Directly proportional to partial pressure of the gas
Henry's Law: C = kHĀ·P, where gas solubility (C) is directly proportional to the partial pressure (P) of the gas above the solution.
Question 4: In electrochemistry, the standard cell potential EĀ°cell is related to the standard Gibbs free energy by:
- ĪGĀ° = nFEĀ°cell
- ĪGĀ° = ānFEĀ°cell (Correct answer)
- ĪGĀ° = RT ln(EĀ°cell)
- ĪGĀ° = nRT/EĀ°cell
Correct answer: ĪGĀ° = ānFEĀ°cell
The relationship is ĪGĀ° = ānFEĀ°cell, where n is moles of electrons transferred and F is Faraday's constant.
Question 5: 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 (azimuthal) quantum number l determines orbital shape: l=0 is s (spherical), l=1 is p (dumbbell), l=2 is d, etc.
Question 6: The Clausius-Clapeyron equation describes the relationship between:
- Reaction rate and temperature
- Vapor pressure and temperature (Correct answer)
- Electrode potential and concentration
- Osmotic pressure and solute concentration
Correct answer: Vapor pressure and temperature
The Clausius-Clapeyron equation relates vapor pressure to temperature using the enthalpy of vaporization.
Question 7: For a second-order reaction with a single reactant, the half-life is:
- Constant and independent of initial concentration
- Directly proportional to initial concentration
- Inversely proportional to initial concentration (Correct answer)
- Proportional to the square root of initial concentration
Correct answer: Inversely proportional to initial concentration
For a second-order reaction, tā/ā = 1/(k[A]ā), meaning half-life decreases as initial concentration increases.
Chemistry Test Physical Chemistry 3
Which of the following best describes the Maxwell-Boltzmann distribution for an ideal gas at higher temperature?