A preliminary half-life check

The thermal decomposition of dinitrogen pentoxide (N2O5) in the gas phase has time-independent stoichiometry 

The half-life for a chemical reaction involving a single reactant can be defined as the time it takes for the concentration of the reactant to fall to one-half of its initial value. (It is important to note that it is not equivalent to one-half the time required for the reaction to go to completion.) 

A kinetic reaction profile for N2O5 measured for the decomposition of this compound in the gas phase at 63.3 °C. A smooth curve is drawn through the experimental data points. 

There is no need to consider the fourth half-life, and so on. 

Successive half-lives for a reaction involving a single reactant A with initial concentration [A]o- 

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A preliminary half-life check of the kinetic reaction profile for NO2 shows that the reaction is not first-order. (You may wish to confirm this for yourself by returning to Exercise 3.1.)... 

A preliminary half-life check has shown that Reaction 3.4 is not first-order. It seems reasonable, therefore, that the next step should be to check whether it is second-order, that is... 

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