Vapour Pressure

[blueST]

You can buy gas canisters for blow torches and the like that contain a propane/butane mix. My vague (and probably wrong) understanding is that these two gases have different vapour pressures, propane being much higher. If that’s the case, when using these cylinder don’t you just get only the propane boiling off and supplying gas until it’s all gone and only then the butane would start to boil off as pressure can fall below its vapour pressure? I’m sure I’m complete
misunderstanding how this all works, but am curious.

[hidetheelephants]

blueST said:

You can buy gas canisters for blow torches and the like that contain a propane/butane mix. My vague (and probably wrong) understanding is that these two gases have different vapour pressures, propane being much higher. If that’s the case, when using these cylinder don’t you just get only the propane boiling off and supplying gas until it’s all gone and only then the butane would start to boil off as pressure can fall below its vapour pressure? I’m sure I’m complete
misunderstanding how this all works, but am curious.

You would if the temperature was below the boiling point of butane, which is -1C; when its above that it's fine.

[WrekinCrew]

Search on " partial pressure"

[blueST]

WrekinCrew said:

Search on " partial pressure"

Had a quick read on Wiki and that seems to answer it, even if I don’t fullly understand. Shamefully I studied all this at Uni 30 years ago, but never used the knowledge and now it’s gone.