The photodissociation of NO₂ by ultraviolet wavelengths of sunlight initiates the formation of photochemical smog. It is a first-order reaction with a rate constant of 2.95 × 10^–3 min^–1 at a given level of light exposure.

Consider a laboratory experiment in which a sample of nitrogen dioxide is exposed to UV radiation at an intensity chosen to mimic conditions for the formation of smog on a summer day. ◂ If the initial concentration of NO₂ is 7.5 mM, what will the concentration be after 2 hours?

Strategy Convert the time given to minutes to match the units of the rate constant and then use the first-order integrated rate law to find [NO₂] at the desired time.  (That mM is just millimolar or 10^-3 M.)

Transcribed Image Text:

NO₂+ hv→ NO + O