English for chemists

Factors Influencing the Rate of Reactions
Every chcmical reaction requires some time for its complctiQn, but some reactions arc very fast and some arc very slow. Reactions between ions in solution without change in oxidation state arc usually extremely fast. An example is the neutralization of an acid by a base, which proceeds as fast as the solutions can be mixed. Presumably nearly every time a hydronium ion collides with a hydroxide ion reaction occurs, and the number of collisions is vciy great, so that there is little delay in the reaction. The formulation of a precipitate, such as that of silver chloridc when a solution containing silver ion is mixed with a solution containing chloridc ion, may require a few scconds, to permit the ions to diffuse together to form the crystalline grains of the precipitate:
Ag*(aq) + Cl'(aq) -» AgCl(c).
On the other hand, ionic oxidation-rcduction reactions arc sometimes very slow. An example is the oxidation of a stannous ion by a fcrric ion:
2FC5* + Sn*’ —» 2Fc2* + Sn4\
This reaction docs not occur every time a stannous ion collides with one or two fcrric ions. In order for a reaction to take place, the collision must be of such a nature that electrons can be transferred from one ion to another, and collisions that permit this electron transfer to occur may be rare.
An example of a reaction that is extremely slow at room temperature is that between hydrogen and oxygen: