Chemistry in Motion

Vakinformatie

Vak van 6 stp gedoceerd door Koen Clays en Jérôme Loreau. Bestaat uit 2 delen: Advanced Chemical Kinetics en Dynamics of Chemical and Biochemical Systems, het laatste deel wordt gedoceerd door Clays en was voordien een vak op zichzelf (kijk naar die examenwikipagina voor oudere vragen). Dynamics of Chemical and Biochemical Systems is een mondeling examen, bevattende hoofdstukken over (1) stabiliteit, (2) fluctuaties, (3) diffusie, (4) Langevin, (5) relaxatie, (6) evolutie. Het laatste hoofdstuk werd de laatste 2 jaar weggelaten.

Examenvragen

12th of January 2024, Morning

Loreau's part

Given a reaction A+B -> C+D, elementary, exothermic, Figure of ln(k(T) w.r.t. 1/T

1. Does this reaction follow Arrhenius behaviour.
2. Why might this reaction deviate from Arrhenius behaviour.
3. Which methods could we use to predict k(T).
4. Assume we use TST what would we need to determine k(T).
5. What are the drawbacks when using TST.

Lindemann’s theory about unimolecular reaction.

1. Describe this theory, write the expression of rate coefficient.
2. What is the problem of this theory and how to fix it?

Cley's part

1. Prove that for stability conditions in terms of entropy can be related to a minimum in "energy".
2. Given is the Master Equation of Fluctuation Theory, for both P(delta P, delta S) and P(delta T, delta V). Derive the amplitude of fluctuations for one of the four possible fluctuations.

29th August 2023

Advanced Chemical Kinetics

First question

Given a Diels-Alder reaction of A+B->C, elementary, exothermic.

• H2C=CH-CH=CH2 (1,3-butadiene) + H2C=CH2 (ethylene) -> H2C=CH-CH2-CH2-CH=CH2 (cyclohexene)

1. Give the order of the reaction, and the unit of the rate coefficient.
2. Describe entropy and enthalpy profile of this reaction.
3. Would you expect the transition state to be more like the reactants or the product?
4. Based on your answer of the previous question, which type of energy is more suitable before the transition state?
5. What methods could be used to describe the rate coefficient? What information do we need to know for each method?
6. If the product further undergoes isomerization or fragmentation, what method should we use for it?

Second question

Lindemann’s theory about unimolecular reaction.

1. Describe this theory, write the expression of rate coefficient.
2. What is the problem of this theory and how to fix it?

Dynamics of Chemical and Biochemical Systems

1. Prove that for stability conditions in terms of entropy can be related to a minimum in "energy".
2. Explain the relation between Fick's laws, Langevin equation and the Einstein equation.

13th January 2023

Advanced Chemical Kinetics

First question

1. Give the rate constant described by TST and explain the different elements.
2. Given are the expressions for Qrot and Qtrans. Qelec and Qvib can be neglected. Describe the temperature dependence for the following reactions:
   • F + H2 --> HF + H
   • C2H4 + HCl --> C2H5Cl
3. What becomes the temperature dependence if we include Qvib.
4. Compare with the result obtained from the Arrhenius equation (A in Arrhenius equation is obtained via experiment whereas with TST the pre-exp. factor is obtained via direct calculation)
5. Can we do quantum calculations for these reactions. Explain

Second question

1. Unimolecular reaction that shows first order behavior at high pressure and second order behavior at low pressure. Write down the reaction rates and the dimensions of the rate constants for these two cases.
2. Prove qualitatively and quantitative the rates at high and low pressure.

Dynamics of Chemical and Biochemical Systems

1. Given is the Master Equation of Fluctuation Theory, for both P(delta P, delta S) and P(delta T, delta V). Derive the amplitude of fluctuations for one of the four possible fluctuations.
2. The reaction is: A+B <-> C+D. Derive and describe the relaxation for an instantaneous T-jump. What are the minimal conditions/requirements and which ones are optimal? (see page 10 of the relaxation pdf)

29th August 2022

Advanced Chemical Kinetics

1. Given the ozone reaction that happens in the earths stratosphere. What method would be the most accurate to describe the rate constant? (justify)
2. Question about TST

1) Write down the expression for the rate constant in TST. Explain the different elements.
2) Given are Qtrans and Qrot equations (Qel and Qvib can be neglected). Describe the temperature dependency of the rate constant for the following reactions (both have non-linear TS):

• F + H2 --> HF + H
• non-linear molecule + linear molecule --> non-linear molecule (Was specific, but don't remember the molecules)

3. Exercise 2.3

Dynamics of Chemical and Biochemical Systems

1. Explain how we get from the entropy maximum of the second law of thermodynamics to the minimum in energy. Explain what role fluctuations play here and explain the probability.
2. Explain the relation between Fick's laws, Langevin equation and the einstein equation. (He said no derivation was necessary) Explain correlation between the diffusion constant and temperature and friction.

14 januari 2022 - Voormiddag

Advanced Chemical Kinetics

1. [NO3] + [CO] --(fast)-> [NO2] + [CO2] bij T hoger dan 255°C; [NO2] + [NO2] --(slow)-> [NO3] + [NO] en [NO3] + [CO] --(fast)-> [NO2] + [CO2] bij T lager dan 255°C (exotherme reacties)

1) Leid voor beide reacties de reactie rate af (tweede met steady state approximation)
2) Wat is de orde van elke reactie en de bijboherende units (2de orde; unit = cm^-3/s)
3) Teken het energieprofiel ifv reactie coordinaat
4) Welke quantum dynamische techniek verkies je: time independent of time dependent? (Time dependent wegens reacties met meer dan 4 atomen. Dit is niet doenbaar voor time independent)
5) Welke technieken zou je nog kunnen gebruiken voor de k te berekenen? (hard sphere, tst, capture theory, classical)
6) Stel de reactie, die exotherm is, heeft een late barrière. Welke energie is nodig voor deze te overbruggen? (Polanyi's rules, E(vibratie) nodig) 

2. Oefening 3 van Chapter 2 met als extra vraag de delen van de k(hard sphere) uit te leggen.

Dynamics of Chemical and Biochemical Systems

1. Gegeven de Master Equation of Fluctuation Theory, voor zowel P(delta P, delta S) als P(delta T, delta V). Leid de amplitude van de fluctuaties van een van deze 2 vergelijkingen af.
2. Reactie A+B <-> C+D. Leid de relaxatieformule af. Wat zijn de minimale condities/voorwaarden en wat zijn de optimale?