# Order of Reaction

The order of reaction may be defined as the sum of the powers to which the concentration (or pressure) terms are raised in order to determine the rate of the reaction.

Therefore, for first order reaction, the expression for the rate of reaction may be given as:

$r = kC_A$

For second order reaction,

$r = kC^2_A \\[3mm] \text{or} \hspace{3mm}r = kC_AC_B$

For third order reaction,

$r = kC^2_AC_B = kC_AC^2_B = kC_AC_BC_C$

All the above terms have usual meaning.

It is important to note that order of reaction is an experimental quantity and it may be a fractional quantity also.

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