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Topic: NO oxidation, negative activation energy?  (Read 3390 times)

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Offline polartownjunkie

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NO oxidation, negative activation energy?
« on: June 16, 2012, 11:28:43 PM »

i am using a chemilluminescense gas analyzer that measures NO, the analyzer measures bottled NO concetrations very well, when diluted entirely with N2.  when i dilute 10% O2 into a NO/N2 sample, i find that the analyzer measures NO quite lower than the true NO concentration.  FTIR sees NO2 forming, and its well known the chemilluminescense detector cant measure NO2.  i read that the oxidation of NO into NO2 has a negative activation energy, such that cold temperatures will increase the oxidation.  at ambient temperatures, am i seeing this reaction occur?  i pass my sample through a 4 Celcius thermoelectric cooler to remove water, is it true this will cause even stronger, more rapid NO oxidation?

thanks!

Offline polartownjunkie

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Re: NO oxidation, negative activation energy?
« Reply #1 on: June 17, 2012, 09:36:36 PM »
im not sure what to make of this temperature dependent 'equilibrium reaction' 
can anyone tell me how to use these equations?

Kc = [(NO)2]/[NO]2
rate = k [NO]2[O2] = k'Kc [NO]2[O2]

if i known sample temperature/flow, NO, NO2, O2 concentrations, can I calculate the amount of NO2? am i missing something?

"the rate of attainment of the equilibrium (Kc) is very fast compared with reaction(k')"
would this mean a change in sample temperature (191C to 4C) would create more NO2 than oxidation of NO and O2

i just want to know if im seeing a real phenomena or if i am misunderstanding the reaction

thanks!

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