Graphical Method: Order and k from Slope and Intercept

Question

In a study of the gas phase decomposition of hydrogen peroxide at 400 °C

H₂O₂(g)H₂O(g) + ½ O₂(g)

the concentration of H₂O₂ was followed as a function of time.

It was found that a graph of 1/[H₂O₂] versus time in seconds gave a straight line with a slope of 0.982 M^-1 s^-1 and a y-intercept of 7.75 M^-1.

Based on this plot, the reaction is _______(zero,first,second) order in H₂O₂ and the rate constant for the reaction is _______M^-1 s^-1.

Answer 1

If a plot of 1/[H₂O₂] vs time gives a straight line, this tells us that the reaction is second order in H₂O₂.

The integrated rate law for a second order reaction is 1/[A] = kt + 1/[A]_o which is the form of a straight line with slope = k.

The answer to the question would be:

The reaction is second order in H₂O₂

The rate constant for the reaction is 0.982 M^-1s^-1