Write the differential rate expression for the following reaction and determine its order of reaction:
$5 Br^{-} + BrO_3^{-} + 6 H^{+} \rightarrow 3 Br_2 + 3 H_2 O$

The differential rate expression is given by:
Rate $= -\frac{1}{5} \frac{d[Br^{-}]}{dt} = -\frac{d[BrO_3^{-}]}{dt} = -\frac{1}{6} \frac{d[H^{+}]}{dt} = \frac{1}{3} \frac{d[Br_2]}{dt} = \frac{1}{3} \frac{d[H_2 O]}{dt}$.
The order of the reaction is $3$ (it is a third-order reaction).