Question

How are reactions classified on the basis of rate of reactions? Give examples.

Answer 1

The rate of different reactions is different. Based on the rate of reactions, the chemical reactions are classified into three categories :

• Instantaneous reactions: The reactions that reach completion within a fraction of a second are called instantaneous reactions.

Example: Burning off some active metals like Sodium $\left(\mathrm{Na}\right)$

$2\mathrm{Na}\left(\mathrm{s}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to {\mathrm{Na}}_2\mathrm{O}\left(\mathrm{s}\right)+\mathrm{Heat}$

• Moderate reactions: The reactions that require time from a few minutes to hours to reach completion are called moderate reactions.

Example: Photosynthesis in plants

$6{\mathrm{CO}}_2\left(\mathrm{g}\right)+6{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\stackrel{\mathrm{Sunlight}}{\to }{\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6\left(\mathrm{aq}\right)+6{\mathrm{O}}_2\left(\mathrm{g}\right)$

• Slow reactions: The reactions that require a longer time ranging from days to months, or even years to reach completion are called slow reactions.

Example: Rusting of Iron $\left(\mathrm{Fe}\right)$

$4\mathrm{Fe}\left(\mathrm{s}\right)+3{\mathrm{O}}_2\left(\mathrm{g}\right)+2\mathrm{x}{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to 2{\mathrm{Fe}}_2{\mathrm{O}}_3.{\mathrm{xH}}_2\mathrm{O}\left(\mathrm{s}\right)$