Question

Express the average rate of the reaction, \[\ce{H2_{(g)} + I2_{(g)} -> 2HI_{(g)}}\], in terms of all reactants and products.

Answer 1

For the reaction \[\ce{H2_{(g)} + I2_{(g)} -> 2HI_{(g)}}\]

The average rate of reaction is expressed as the change in concentration of reactants or products per unit time. It is written as:

\[\ce{Average rate = -\frac{1}{t} \frac{d[H_2]}{dt}}\]

= \[\ce{-\frac{d[I_2]}{dt}}\]

= \[\ce{\frac{1}{2} \frac{d[HI]}{dt}}\]

The minus sign indicates that the concentration of reactants decreases with time. The coefficient 1/2 in the HI term accounts for the stoichiometry (since 2 moles of HI are formed per mole of H₂ or I₂ consumed).