D.I. Mendeleev A.M.Butlerov

The velocity of chemical reactions
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Influence of temperature on the velocity. Additional material.

The rule of Vant-Hoff

The rule of Vant-Hoff is no more than rule it has no validity of the law.

First, Vant-Hoff could study chemical reactions in the bounded conditions which were provided by laboratory technical equipment of that time. As it was found out later, the temperature factor can change in a significant temperature interval.

Besides because of imperfection of technical means it was impossible to study as very fast reactions (proceeding in milliseconds), and very slow ones(for which thousand years are required). Reactions with participation of greater molecules of the complex form (for example, proteins) also do not submit to the rule of Vant-Hoff.

The energy of activation

Molecule is energetically advantageous formation (otherwise no molecules would exist). It means, that chemical substances on the energy diagram occupy positions in "wells".

the energy of activation

If we wish to carry out a reaction, i.e. to transform these substances into others, we should give sufficient energy to the reagents to surpass the "barrier" (energy of activation).

For this purpose, as a rule, it is required to heat up a reaction mix to the certain temperature to increase the kinetic energy of molecules. If the energy barrier of a reaction is low then an impact or friction is enough for its beginning.



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