For the first-order reaction 2N2O5(g) -> 4NO2(g) + O2(g), which of the following statements is correct?

The reactant concentration decreases exponentially with time.
The half-life of the reaction increases with increasing temperature.
The half-life of the reaction depends on the initial concentration of the reactant.
The reaction goes to about 87.5% completion in three half-lives only.

Correct answer: The reactant concentration decreases exponentially with time.

Solution

For first-order kinetics the concentration falls off exponentially with time, and the half-life is independent of initial concentration and decreases with rising temperature. Hence the only correct statement is that concentration decreases exponentially with time.

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