In a study of formation of HI from its elements,
${\mathbf{H}}_{\mathbf{2}}\mathbf{\left(}\mathbf{g}\mathbf{\right)}\mathbf{+}{\mathbf{I}}_{\mathbf{2}}\mathbf{\left(}\mathbf{g}\mathbf{\right)}\mathbf{\rightleftharpoons }\mathbf{2}\mathbf{HI}\mathbf{\left(}\mathbf{g}\mathbf{\right)}$

Equal amounts of hydrogen and iodine were placed in a container which was then sealed and heated.

(a) On one set of axes, sketch concentration vs. Time curves for hydrogen and hydrogen iodide, and explain how Q changes as a function of time.

(b) Is the value of Q different if [iodine] is plotted instead of [hydrogen]?

The reaction quotient is the ratio of concentration of products to the reactants raised to their coefficient powers. This gives the relative amount of substances present in a chemical reaction. It is represented by the letter ‘Q’.

The graph is as shown below.

The concentration of reactant decreases with time and the concentration of product increases with time.

The reaction quotient Q increases with respect to the increase in concentration of product and decrease with increase in concentration of reactants with time.

The given reaction for the formation of HI shows that one mole of hydrogen react with one mole of iodine to give . The concentration of hydrogen and iodine varies in a similar way.

Hence, on plotting the graph with concentration of iodine instead of concentration of hydrogen vs. time, we get the same plot.