Physical Chemistry (II) Mid-Term Exam
(2023-10-26, Chung-Ang University, Prof. Sol Ahn’s Class)
*State any assump-ons you make. Try to answer as much as you can to earn par-al credits.
1. (20pts) Determine whether following statements are true or not. If not, correct a statement
and there will be penalty if you don’t state anything in case a statement is wrong.
(1) You can obtain the rate of effusion by using the collision flux expression.
(2) Stokes-Einstein equa-on provides a rela-on between diffusivity and viscosity.
(3) It is not possible to extrapolate the conclusions to neutral molecules (zero charge) by
studying the transport of charge through electrolyte solu-ons.
(4) When you need a strong mixing in the solu-on, convec-on is not required as diffusion is a
very fast process.
(5) Reac-on order can have non-integer values.
(6) The half-life of the 1st order reac-on depends on the ini-al concentra-on of the reactant.
(7) The rate-determining step is the fastest step in a reac-on mechanism.
(8) You cannot prove a reac-on mechanism under any circumstances.
2. (10 pts) In the “Phenomenological Equa-on”, there are three types of transport. What are
they? What is a driving force for each (you should include sign, and explain why it’s either
posi-ve or nega-ve) and coefficients of propor-onality (please include unit)?
3. (15 pts) Calculate the frequency of H2-H2 collisions in a 1.0 cm3 container at 1.0 bar and 298
K. What is the mean free path of H2? What does it mean here?
Collision cross-sec-on of H2 2.3 × 10-19 m2, M.W. of H2: 2.016 g mol-1
Boltzmann constant 1.38 × 10-23 J K-1, 1 bar = 105 N m-2, R = 8.314 J mol-1 K-1
4. (15 pts) Describe the difference between Fick’s 1st law and 2nd law. Also, explain what each
term means (you should men-on unit of them as well) in Fick’s 2nd law of diffusion with
appropriate Figure (You can just men-on something like “Figure XX from the textbook”).
5. (20 pts) Please answer following ques-ons.
(1) A reac-on is reported to have an ac-va-on energy of 45 kcal mol-1. By what factor will the
rate constant increase between 298 K and 308 K? What is the corresponding increase if the
ac-va-on energy is 30 kcal mol-1 for the same temperature increase (298 K to 308 K)?
(2) For a given reac-on, the rate constant doubles when the temperature is increased from
25 °C to 35 °C. What is the Arrhenius ac-va-on energy for this reac-on?
6. (20 pts) The rate of following reac-on decreases with increasing temperature. Explain the
reason why it decreases with increasing temperature. (Here, NO3* is the intermediate)
The reac-on:
2NO + O2 → 2NO2
The rate law:
rNO2 = kr[NO]2[O2]
Mechanism:
NO + O2 → NO3*
NO3* → NO + O2
NO3* + NO → 2NO2
k1
k2
k3