Question

What is a slow & fast reaction? Give examples.

Answer 1

The study of the rate of chemical reaction & the mechanism by which the reaction occurs comes under chemical kinetics. The kinetics studies deal with the study of reaction rates or velocity of reaction.

Complete answer:
Types of reaction based on rates:

Fast reaction: This type consists of reactions which occur almost instantaneously. These types of reactions involve ionic species and complete in a few seconds.
Examples: The precipitation of $AgCl$ occurs instantaneously on addition of aqueous solution of sodium chloride to aqueous addition of silver nitrate.

$AgN{O_3}\left( {aq} \right) + NaCl\left( {aq} \right) \to AgCl\left( s \right) + NaN{O_3}\left( {aq} \right)$

The reaction between sodium & ${H_2}O$ (water) to form sodium hydroxide occurs at a very fast rate.

$2Na\left( s \right) + 2{H_2}O\left( l \right) \to 2NaOH\left( {aq} \right) + {H_2}\left( g \right)$

Combustion reaction like burning of fuel in air or oxygen is a very fast reaction.

Slow reaction: This type of reactions which occur at a very slow rate & may require months & years together for completion.
Examples:
i) Rusting of Iron is a slow reaction
ii) Weathering of rocks is an extremely slow reaction
iii) The fermentation of sugar to alcohol is quite slow.

Note: The rates of fast reactions (ionic reactions) cannot be determined easily.
It is because in such reactions no chemical bonds are to be broken among the reactants.
The rates of slow reaction are hardly of any physical significance.