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C. Y. Yeung (CHW, 2009) p.01 Maxwell- Boltzmann Distribution & Collision Theory Interpretation of Rate of Gaseous Rxn at Molecular Level.

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Presentation on theme: "C. Y. Yeung (CHW, 2009) p.01 Maxwell- Boltzmann Distribution & Collision Theory Interpretation of Rate of Gaseous Rxn at Molecular Level."— Presentation transcript:

1 C. Y. Yeung (CHW, 2009) p.01 Maxwell- Boltzmann Distribution & Collision Theory Interpretation of Rate of Gaseous Rxn at Molecular Level

2 No. of Effective Collisions  Rate of Rxn  p.02 Factors affecting the Rate of Rxn …? Temperature Conc. / Pressure Surface Area Catalyst Kinetic energy of particles  Frequency of Collisions  Areas of Contact  No. of Collisions  Rxn occurs via a pathway with a lower E a Effective Collisions  Collision Theory 1.Molecules with K.E.  E a, and 2.Collide in right orientation.

3 p.03 Conc. / Pressure Frequency of Collisions  Frequency of Collisions is Important ! Molecules have different Kinetic Energy (K.E.) During collisions, some molecules gain energy from the others, and some molecules loss energy to the others. i.e. Distribution of K.E. of molecules in a system

4 p.04 In the system, molecules have a range of K.E. Maxwell-Boltzmann Distribution Molecules with “most probable speed” Area under curve  total no. of molecules No. of molecules with K.E.  E a  rxn occurs! Distribution of K.E. at temperature = T 1

5 no. of molecules p.05 Distribution of K.E. at Different Temperature ? Areas under curve 0 0 C, 25 0 C and C are the same ! (no. of molecules in system remains constatnt) Temp. , more molecules take part in rxn.  rate of rxn .  rate of rxn . EaEaEaEa

6 p.06 Explain how temp. affects the Rate of Rxn … Temp.  Collision Frequency  Energy transfer between molecules becomes more frequent. Wider distribution of K.E. No. of molecules have K.E.  E a  No. of molecules take part in rxn  Rate of Rxn 

7 p.07 p. 77 Q.4 ( M-B Distribution) As temp. , fraction of molecules with high K.E. . Hence, force exerted by the collision of molecules on the container wall .

8 p.08 p. 78 Q.7(b) ( M-B Distribution) As a higher temp., the portion towards high K.E. is much larger. More molecules would have sufficient energy to overcome E a and to react. Increasing the number of effective reactant increases the rate of reaction.

9 p.09 Catalyst & M-B Distribution: Catalyst provides an alternative pathway for the reaction to occur. Positive Catalyst provides a pathway with lower E a. E a ’ (catalysed) E a (uncatalysed)

10 p.10 Conclusion 5 factors affecting the rate of reactions (with explanations in terms of frequency of effective collisions. [Collision Theory] Maxwell-Boltzmann Distribution of Molecular Speeds and Kinetic Energy Explain how temperature change and use of catalyst affect the rate of reaction with Maxwell-Boltzmann Distribution

11 p.11 Next …. Single / Multi-stage Reaction & Energy Profile, Catalyst (p )

12 p.12 Assignment Pre-lab: Expt. 9 Determination of Activation Energy [due date: 26/2(Thur)] p. 53 Check point 15-1 p. 58 Check point 15-2 [due date: 26/2(Thur)]


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