[Peng Zhong]

Hi experts,

If I have a test tube of NO2/N2O4 mixture and heat it up to high temperature so that the equilibrium shifts to favor the formation of NO2. Now the NO2 concentration is near 100%. Then I quenched the test tube in ice water so the temperature drop rapidly until it hits room temperature of 20C. Because the cooling is so fast, the NO2 didn't react fast enough to form N2O4, so the concentration of NO2 is still close to 100%. Now if I quickly insulate the test tube  so that no heat can transfer out of the test tube. Will the mixture (still near 100% NO2 after insulated) in test tube form N2O4 in this adiabatic condition? We know that formation of N2O4 require heat transfer out of the system so insulating it might stop the equilibrium and keep NO2 at near 100% concentration even at room temperature. Am I correct?

Thanks.

[mjc123]

No, you will still get N₂O₄ formed, but the heat released will raise the temperature of the insulated system rather than being lost to the surroundings. (Which means the position of equilibrium will be slightly different.)

[Arkcon]

Hi experts,

If I have a test tube of NO2/N2O4 mixture and heat it up to high temperature so that the equilibrium shifts to favor the formation of NO2. Now the NO2 concentration is near 100%.

With you so far ...

Then I quenched the test tube in ice water so the temperature drop rapidly until it hits room temperature of 20C.

Sounds like a cool experiment ...

Because the cooling is so fast, the NO2 didn't react fast enough to form N2O4, so the concentration of NO2 is still close to 100%.

And now you lost me.  I don't believe a test tube of anything will cool faster than this reaction can happen.  Maybe a capillary tube might come to temperature enriched slightly, but not likely.  Now if you could cool a sample with cryogenic liquid, freezing it solid, maybe you can keep it enriched.

Now if I quickly insulate the test tube  so that no heat can transfer out of the test tube. Will the mixture (still near 100% NO2 after insulated) in test tube form N2O4 in this adiabatic condition? We know that formation of N2O4 require heat transfer out of the system so insulating it might stop the equilibrium and keep NO2 at near 100% concentration even at room temperature. Am I correct?

Nothing insulates that perfectly.