[Helpmeplzz]

Hello, i have a question about my previous examination i was asked the following question:

You have 2 jars next to each other. The one on the left is filled with Bromine gas, the one of the right with Potassium gas. A haze/fog forms above the jars. Show whether the haze is slightly more to the left or to the right side. What reaction could this be ?

[Corribus]

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[Helpmeplzz]

This is what i got so far:

A possible reaction could be 2K+Br2 → 2KBr. You need 2 times more K then Br2. According to Le Chatelier principle the equilibrium would shift to the right and therefore the haze would be more abundant on the right.

[MNIO]

you have a jar of Br2 gas on the left and a jar of.... what was that?. potassium metal on the right???  and a haze forms over the jars?  where did you get this problem from?

some things to think about
  (1) if you have two substances that diffuse through a vapor phase and meet somewhere
       in between and then react, where will they meet?  (think which diffuses faster)
  (2) graham's law.
  (3) potassium metal? 

[Helpmeplzz]

The second jar contains potassium gas.

[Helpmeplzz]

When i apply graham's law on this problem i find that K diffuses faster than Br because of its molar mass being smaller. This would therefore mean that there would be more haze on the right. Correct ?

EDIT: haze is translated using google translate i have no clue what the actual correct word for it is in english. Other translations are fog/nebula. I should also mention that the question stated that this cloud/fog/nebula was white.

[Corribus]

I think the diffusion rate is what they're going for here. It's a bit of a weird problem because it's so unrealistic. Just remember, the reaction will occur farther from where the faster diffusing gas is located.

[AWK]

The problem is undefined. At the boiling point of bromine (vapor pressure 760 mmHg), the vapor pressure of potassium is about 10^-6 mmHg. If we obtained a vapor pressure of both elements of 760 mmHg, then at the moment of contact of the gases as a result of a strongly exothermic reaction, an explosion would probably occur, or a process so turbulent that speaking about diffusion or Graham's law does not make sense.
There are so many real and interesting problems and experiences in chemistry - inventing such absurd processes causes that students, instead of liking chemistry, are afraid of it or hate it.

[MNIO]

ahh AWK.. I totally agree with you.

Helpmeplzz.. the reason I'm astounded by this question is
  (1) the melting point of potassium metal is 146°F
  (2) the bp of potassium is 1400°F
  (3) I doubt your jar would stand up to that temperature
  (4) I doubt you or your lab would survive such a phenomena (K would react with stuff
       like.. oh.. moisture.. quite rapidly at that temp)
  (5) grahams law is based on the assumption that KE is only dependent on T
        this is an ideal gas assumption that breaks down at high T's

etc
**********
The whole idea of this question is to make you think about how fast vapors will diffuse.  The higher the molar mass, the lower the diffusion rate.  And I've heard this question asked a dozen different ways.  HCl in 1 bottle and NH3OH in another, for example.  But for you to consider two chemicals meeting and reacting in the vapor phase, well.. they both need to be in the vapor phase don't they?

and potassium metal with vapor pressure ≈ 0 doesn't work does it?

[nikkinemo95]

One way to make potassium bromide is to react the hydroxide with hydrobromic acid. ... While not a normal route of preparation because of the expense, potassium metal reacts vigorously with all the halogens to form potassium halides

[Enthalpy]

If the second jar contains potassium gas, I expect it to detonate upon opening it to air.

Even if said jar contained potassium at low pressure and temperature in a neutral carrier gas like argon, potassium would immediately react with air's moisture, and then no gaseous diffusion holds.

Maybe it's the sought answer: haze is hydrated KOH. Or more probably, the question is meaningless.