For the reaction NO + O3 NO2 + O2 the second order rate constant has a value of

Question

For the reaction NO + O3 NO2 + O2 the second order rate constant has a value of 1.8x10^-14 molecule-1 cm3 s-1 at 25°C. The concentration of NO in a relatively clean atmosphere is 0.10 ppbv (parts per billion by volume) and that of O3 is 15 ppbv. Calculate these two concentrations in units of molecule cm-3. Calculate the rate of the NO oxidation using concentration units of molecule cm-3. Show how the rate law may be expressed in pseudo-first-order terms and calculate the corresponding pseudo-first-order rate constant. Assume the reaction occurs at a pressure of 1 atm.

Explanation / Answer

a) PV = nRT

[M] = n/V= P/RT

[M] = 2.46*10^9 molecules/cm3 = Concentration of NO

[M] = 3.69*10^11 molecules/cm3 = Concentration of O3

b) Rate of oxidation of NO:

Rate NO = k2[NO][O3]

Rate NO =1.63*107 molecules/sec* cm3

c)If we assume the concentration of O3 is unchanging during the reaction (since its concentration is more than 100 times that of NO), we can treat this value as constant. We can

than combine the two constants and derive the new rate constant k’ (pseudo first order constant with units s-1)

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