Any question answered...

When did you start? Ambient pressure in London is up about 10mb since midday Friday
https://barometricpressure.app/london

The reaction is endothermic so absorbs the heat whilst reacting. Therefore it ultimately shrinks back and will be colder. Get the thermometer out and add another aspect to the experiment.

nvm

Carbon dioxide is also soluble in water so perhaps has been reabsorbed? As above, atmospheric pressure is could well be a factor. In the middle of the recent storms I noticed the difference in some ziplock bags that I'd sealed some time before.

Cheers all.

We did it on Wednesday afternoon.

Wednesday afternoon

That should rule out ambient if the pic is from today, very little difference between Wed PM and now in London.

Carbon dioxide is also soluble in water so perhaps has been reabsorbed?

I would expect the dissolved gas concentration to be close to equilibrium immediately after the experiment, since the decomposition of H₂CO₃ generated in the first stage of the reaction happens in an almost ideal way to maximise solution of the resulting CO₂ in the water.

To the extent that the reaction chills the solution due to the slight overall endothermicity, the equilibrium concentration of dissolved CO₂ should fall as the temperature equilibrates to ambient, so more gas should come out of solution.

My guess:

The balloon inflates because the pressure inside is greater than outside. Then some air is lost through the balloon material itself or the seal at the neck. Then it cools down and the amount of air inside is reduced compared to when you started so you get the effect you've seen.

Then it cools down

By what mechanism? We've generally agreed that dilute ethanoic acid and sodium hydrogen carbonate reacting to generate carbon dioxide gas is a net endothermic process, so the "inflated" condition early in the process is below or at best at ambient temperature. We know that in the inflated condition, there's a pressure and concentration gradient across the balloon membrane driving diffusion, so the pressure in the reaction vessel should slowly equilibrate to ambient.

In the case of a butyl rubber balloon, the rubber should dissolve carbon dioxide, which might generate a pressure slightly below ambient since the reaction vessel gas volume would be highly enriched in CO₂ before being sealed. this would rely on solution of CO₂ in rubber happening faster than diffusion of atmospheric air back into the reaction vessel to replace it. We need more measurements, at least time plots of temperature and pressure inside and outside the reaction vessel, and maybe the composition of the gas in the reaction vessel.

What tester said.

Is there an e-bike thread on here? Like 'what e-bike should i buy?' kind of thing.

https://www.lfgss.com/conversations/164941/newest/

Many thanks! Amazingly in my roughly 4 different search terms i never thought to actually use the word 'electric'.

What do airport fire crews do all day? I’m sure there’s training, drills and maintenance but there can’t be as much to do as a ‘regular’ fire crew?

They rescue cats stuck on top of the control tower.

At a small airport I once went through, baggage handling. They had to be on standby when aircraft were taking off and landing but since that was a plane an hour they had lots of time to do other stuff.

Just by way of an update the pressure has increased and the balloon is now partially inflated inside the bottle.

Before:

After:

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(carpenter's pencil is not pertinent)

Where can I buy corn tortillas in north London? Preferably north east and something authentic

No wheat is essential

Mestizo? https://mestizomarket.com/ Maybe not north enough.

We found that Planet Organic stocks proper corn tortillas

https://www.planetorganic.com/search?q=Cool%20Chile

They even had blue ones in the Muswell Hill Store

Ooo thanks, may be worth a trip.

never tried blue. Thanks for the tip

Anyone able to take a guess as to what RAL code this might be?

I owned this bike and specified the paint as RAL 7031. Now I'm looking to get another frame powder coated, but the person doing the coating thinks it doesn't look like 7031. I can confirm it was quite blue in real life.

Obviously standard caveats about how colours don't look right on screen etc.

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7031 does appear to be greyer, summat like 5023?