chemistry technology

Every chemical reaction requires some time for its completion, but some reactions are very fast and others  very  slow.  Reactions  between  ions  in  solution  without  change  in  oxidation  state  are  usually extremely  fast.  An  example  is  the  neutralization  of  an  acid  by  a  base,  which  proceeds  as  fast  as  the solutions  can  be  mixed.  Presumable  nearly  every  time  a  hydronium  ion  collides  with  a  hydroxide  ion reaction occurs, and the number of collisions is very great, so that there is little delay in the reaction. The formation of a precipitate, such as that of silver chloride when a solution containing silver ion is mixed with a solution containing chloride ion, may require a few seconds, to permit the ions to diffuse together
to form the crystalline grains of the precipitate. On the other hand, ionic oxidation-reduction reactions are sometimes very slow. An example is the oxidation of stannous ion by ferric ion. This reaction does not occur  every  time  a  stannous  ion  collides  with  one  or  two  ferric  ions.  In  order  for  the  reaction  to  take place, the collision must be of such a nature that electrons can be transferred from one ion to another, and collisions, which permit this electron transfer to occur, may be rare.
The factors, which determine the rate of a reaction, are manifold. The rate depends not only upon
the  composition  of  the  reacting  substances,  but  also  upon  their  physical  form,  the  intimacy  of  their mixture, the temperature and pressure, the concentrations of the reactants, special physical circumstances such as irradiation with visible light, ultraviolet light, X-rays, neutrons, or other waves or particles, and
the presence of other substances which affect the reaction but are not changed by it/catalysts/.
Most actual chemical processes are very complicated, and the analysis of their rate is very difficult.
As reaction proceeds the reacting substances are used up and new ones are formed; the temperature of the system is changed by the heat evolved or absorbed by the reaction; and other effects may occur which influence  the  reaction  in  a  complex  way.  For  example,  when  a  drop  of  a  solution  of  potassium permanganate  is  added  to  a  solution  containing  hydrogen  peroxide  and  sulfuric  acid  no  detectable reaction may occur for several minutes. The reaction speeds up, and finally the rate may become so great
as  to  decolorize  a  steady  steam  of  permanganate  solution  as  rapidly  as  it  is  poured  into  the  reducing
solution.  This  effect  of  the  speeding  up  of  the  reaction  is  due  to  the  vigorous  catalytic  action  of  the products of permanganate ion reduction: the reaction is rapidly accelerated as soon as they are formed.