The role of positive catalysts.
Positive catalyst works as an alternative to reaction or by the formation of a transition (intermediate) compound with low activation energy. The activation energy of this path is lower. As a result, the reaction rate increases.
The role of negative catalysts.
The negative catalyst does not reduce activation energy, but rather combines with reactive molecules, thus reducing the number of reactive molecules that collide. This reduces effective collisions and therefore the reaction rate.
Light or Radiation
Not all reactions are affected by light or radiation, but there are few reactions that usually affect light by free radicals or photochemical reactions. Light activates some reactive molecules that release free radicals. Because the free radicals are so depleted, they react with other molecules to form products. The concentration of the reagents does not affect the rate of such reactions, so they are a zero-order reaction. We know that light consists of a photon. When photons hit the reactive molecule, they give the reactive molecules the activation energy they need.
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