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:
C. Y. Yeung (CHW, 2009) p.01 Maxwell- Boltzmann Distribution & Collision Theory Interpretation of Rate of Gaseous Rxn at Molecular Level
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.
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
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
no. of molecules p.05 Distribution of K.E. at Different Temperature ? Areas under curve 0 0 C, 25 0 C and 100 0 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
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
p.07 p. 77 Q.4 (1996 --- M-B Distribution) As temp. , fraction of molecules with high K.E. . Hence, force exerted by the collision of molecules on the container wall .
p.08 p. 78 Q.7(b) (1998 --- 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.
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)
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
p.11 Next …. Single / Multi-stage Reaction & Energy Profile, Catalyst (p. 58-69)
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)]