Collision Theory of Reaction Rates Quiz

1
Collision Theory of Reaction Rates Quiz

• Consider the following two reactions
• F (g) F (g) ------gt F2 (g)
• and
• Cl (g) Cl (g) ------gt Cl2 (g)
• bond length of F2 140 pm
• bond length of Cl2 200 pm
• For these reactions
• k 25/2 p No r2 8 k T / p m1/2 e1/2
  (steric factor) e - Ea / R T
• a. According to collision theory will the rates
  of these reactions increase or decrease with
  increasing temperature and why?
• Increasing T will increase both the 8 k T / p
  m1/2 and e - Ea / R T terms and increase the
  reaction rate.
• According to collision theory and assuming that
  the energies of activation and steric factors are
  the same for these two reactions, which reaction
  would you expect to be faster at a given
  temperature and why?
• r2 / m1/2 F / r2 / m1/2 Cl
• (140 pm)2 / (19.00)1/2 F / (200 pm)2 /
  (35.45)1/2 )Cl
• 4.50 103 / 6.72 103 0.669
• The reaction between Cl atoms should be faster.

2

• Both of these reactions are very fast why?
• Both F and Cl are free radicals with
  essentially no
• activation energy to overcome in order to react!