PHYSICAL CHEMISTRY IN BRIEF

CHAP. 9: CHEMICAL KINETICS [CONTENTS] 313

9.5.10 Radical polymerization

Radical polymerization is a special case of a chain reaction in which a monomer molecule M

reacts with a polymer radical M·n,whose chain permanently grows. In the stage of propagation,

the following reactions take place

M

+ M → M 2

,

M 2

+ M → M 3

,

Mn·+ M → Mn+1·. (9.154)

9.5.11 Photochemical reactions

Photochemical reactions are initiated by electromagnetic radiation. This type of reactions
comprises photosynthesis, the reaction causing the tanning of the skin during sunbathing,
photographic processes, and a number of organic syntheses.

9.5.11.1 Energy of a photon

The Planck relation applies for this energy

=hν=h

c

λ

=hcν , ̃ (9.155)

wherehis the Planck constant,cis the light velocity,νis the frequency,λis the wave length,
and ̃νis the radiation wavenumber.

Example

Light of the wave lengthλ= 299.3 nm was supplied to a system. The system absorbed 10 J of

energy. How many photons were absorbed?