Even the simplest science experiment can require careful reasoning.
Eg.
Place a lit candle on end in a pool of water. Upend a beaker over the top trapping a column of air 10 cm high. As the candle burns it uses up oxygen until it stops burning. When the experiment has cooled overnight, how much has the water level in the beaker risen?
mollwollfumble said:
Even the simplest science experiment can require careful reasoning.Eg.
Place a lit candle on end in a pool of water. Upend a beaker over the top trapping a column of air 10 cm high. As the candle burns it uses up oxygen until it stops burning. When the experiment has cooled overnight, how much has the water level in the beaker risen?
The water level will rise because of cooling (the air in the beaker was warm, but will cool once the candle goes out, reducing the volume of gas).
The number of moles of CO2 produced will be the same as the number of O2 molecules so the n won’t be much changed.
(Technically there will be a change in n because of evaporation, and also because some CO was produced, but these will not be enough to produce a significant change compared to the temperature effect mentioned above.)
dv said:
mollwollfumble said:
Even the simplest science experiment can require careful reasoning.Eg.
Place a lit candle on end in a pool of water. Upend a beaker over the top trapping a column of air 10 cm high. As the candle burns it uses up oxygen until it stops burning. When the experiment has cooled overnight, how much has the water level in the beaker risen?
The water level will rise because of cooling (the air in the beaker was warm, but will cool once the candle goes out, reducing the volume of gas).
The number of moles of CO2 produced will be the same as the number of O2 molecules so the n won’t be much changed.
(Technically there will be a change in n because of evaporation, and also because some CO was produced, but these will not be enough to produce a significant change compared to the temperature effect mentioned above.)
Close but no cigar. Would you like to try again?
mollwollfumble said:
dv said:
mollwollfumble said:
Even the simplest science experiment can require careful reasoning.Eg.
Place a lit candle on end in a pool of water. Upend a beaker over the top trapping a column of air 10 cm high. As the candle burns it uses up oxygen until it stops burning. When the experiment has cooled overnight, how much has the water level in the beaker risen?
The water level will rise because of cooling (the air in the beaker was warm, but will cool once the candle goes out, reducing the volume of gas).
The number of moles of CO2 produced will be the same as the number of O2 molecules so the n won’t be much changed.
(Technically there will be a change in n because of evaporation, and also because some CO was produced, but these will not be enough to produce a significant change compared to the temperature effect mentioned above.)
Close but no cigar. Would you like to try again?
No, I’ve have my turn.
I’ve got what seems to be the correct answer, but I had to Binge to get it, so I won’t post it yet.
I’d say it comes under the “should be bleedin’ obvious, but isn’t” category.
Also under the “why isn’t this better known” category.
dv said:
mollwollfumble said:
dv said:The water level will rise because of cooling (the air in the beaker was warm, but will cool once the candle goes out, reducing the volume of gas).
The number of moles of CO2 produced will be the same as the number of O2 molecules so the n won’t be much changed.
(Technically there will be a change in n because of evaporation, and also because some CO was produced, but these will not be enough to produce a significant change compared to the temperature effect mentioned above.)
Close but no cigar. Would you like to try again?
No, I’ve have my turn.
Wasn’t the beaker upended?
The Rev Dodgson said:
I’ve got what seems to be the correct answer, but I had to Binge to get it, so I won’t post it yet.I’d say it comes under the “should be bleedin’ obvious, but isn’t” category.
Also under the “why isn’t this better known” category.
Chastened by moll’s response, I took to Google as well.
Harvard University:Getting the facts right
When the oxygen is depleted, the candle goes out and the air cools. The volume of the air decreases and the water rises.
Of course, it is possible the Internet and Me are both wrong, so I’ll be very interested in hearing the correct answer.
dv said:
The Rev Dodgson said:
I’ve got what seems to be the correct answer, but I had to Binge to get it, so I won’t post it yet.I’d say it comes under the “should be bleedin’ obvious, but isn’t” category.
Also under the “why isn’t this better known” category.
Chastened by moll’s response, I took to Google as well.
Harvard University:Getting the facts right
When the oxygen is depleted, the candle goes out and the air cools. The volume of the air decreases and the water rises.Of course, it is possible the Internet and Me are both wrong, so I’ll be very interested in hearing the correct answer.
No worries, I’ll have a look at it when I get some time.
Later today or tomorrow.
Peak Warming Man said:
dv said:
The Rev Dodgson said:
I’ve got what seems to be the correct answer, but I had to Binge to get it, so I won’t post it yet.I’d say it comes under the “should be bleedin’ obvious, but isn’t” category.
Also under the “why isn’t this better known” category.
Chastened by moll’s response, I took to Google as well.
Harvard University:Getting the facts right
When the oxygen is depleted, the candle goes out and the air cools. The volume of the air decreases and the water rises.Of course, it is possible the Internet and Me are both wrong, so I’ll be very interested in hearing the correct answer.
No worries, I’ll have a look at it when I get some time.
Later today or tomorrow.
We appreciate that you are a busy man.
dv said:
The Rev Dodgson said:
I’ve got what seems to be the correct answer, but I had to Binge to get it, so I won’t post it yet.I’d say it comes under the “should be bleedin’ obvious, but isn’t” category.
Also under the “why isn’t this better known” category.
Chastened by moll’s response, I took to Google as well.
Harvard University:Getting the facts right
When the oxygen is depleted, the candle goes out and the air cools. The volume of the air decreases and the water rises.Of course, it is possible the Internet and Me are both wrong, so I’ll be very interested in hearing the correct answer.
That’s the link I was looking at.
It does say that the thermal expansion and cooling is not the only mechanism at work.
dv said:
The Rev Dodgson said:
I’ve got what seems to be the correct answer, but I had to Binge to get it, so I won’t post it yet.I’d say it comes under the “should be bleedin’ obvious, but isn’t” category.
Also under the “why isn’t this better known” category.
Chastened by moll’s response, I took to Google as well.
Harvard University:Getting the facts right
When the oxygen is depleted, the candle goes out and the air cools. The volume of the air decreases and the water rises.Of course, it is possible the Internet and Me are both wrong, so I’ll be very interested in hearing the correct answer.
The Rev Dodgson said:
dv said:
The Rev Dodgson said:
I’ve got what seems to be the correct answer, but I had to Binge to get it, so I won’t post it yet.I’d say it comes under the “should be bleedin’ obvious, but isn’t” category.
Also under the “why isn’t this better known” category.
Chastened by moll’s response, I took to Google as well.
Harvard University:Getting the facts right
When the oxygen is depleted, the candle goes out and the air cools. The volume of the air decreases and the water rises.Of course, it is possible the Internet and Me are both wrong, so I’ll be very interested in hearing the correct answer.
That’s the link I was looking at.
It does say that the thermal expansion and cooling is not the only mechanism at work.
Which I said, too.
It’s just the dominant one.
Tamb said:
dv said:
The Rev Dodgson said:
I’ve got what seems to be the correct answer, but I had to Binge to get it, so I won’t post it yet.I’d say it comes under the “should be bleedin’ obvious, but isn’t” category.
Also under the “why isn’t this better known” category.
Chastened by moll’s response, I took to Google as well.
Harvard University:Getting the facts right
When the oxygen is depleted, the candle goes out and the air cools. The volume of the air decreases and the water rises.Of course, it is possible the Internet and Me are both wrong, so I’ll be very interested in hearing the correct answer.
Is CO2 more or less soluble in water than O2?
Like for like, CO2 is about twice as soluble in water. But we’re talking about much less than 1 part per thousand, still: the water is not going to dissolve enough oxygen or carbon dioxide to make an effect that is similar to the effect of the cooling.
dv said:
The Rev Dodgson said:
dv said:Of course, it is possible the Internet and Me are both wrong, so I’ll be very interested in hearing the correct answer.
That’s the link I was looking at.
It does say that the thermal expansion and cooling is not the only mechanism at work.
Which I said, too.
It’s just the dominant one.
You said that there would be about the same number of molecules in the air after combustion, which as far as I can see isn’t right at all.
The Rev Dodgson said:
dv said:
The Rev Dodgson said:That’s the link I was looking at.
It does say that the thermal expansion and cooling is not the only mechanism at work.
Which I said, too.
It’s just the dominant one.
You said that there would be about the same number of molecules in the air after combustion, which as far as I can see isn’t right at all.
I then mentioned carbon monoxide and water vapour, which are going to be the major causes for variation.
dv said:
Tamb said:
dv said:Of course, it is possible the Internet and Me are both wrong, so I’ll be very interested in hearing the correct answer.
Is CO2 more or less soluble in water than O2?Like for like, CO2 is about twice as soluble in water. But we’re talking about much less than 1 part per thousand, still: the water is not going to dissolve enough oxygen or carbon dioxide to make an effect that is similar to the effect of the cooling.
Tamb said:
dv said:
Tamb said:Is CO2 more or less soluble in water than O2?
Like for like, CO2 is about twice as soluble in water. But we’re talking about much less than 1 part per thousand, still: the water is not going to dissolve enough oxygen or carbon dioxide to make an effect that is similar to the effect of the cooling.
I must be missing something. The water starts and finishes at the same temperature so cooling will make no difference because the water will return to it’s original temp.
“The water starts and finishes at the same temperature”
The GAS is hot when you seal with the beaker. The GAS cools when the candle goes out.
dv said:
The Rev Dodgson said:
dv said:Which I said, too.
It’s just the dominant one.
You said that there would be about the same number of molecules in the air after combustion, which as far as I can see isn’t right at all.
I then mentioned carbon monoxide and water vapour, which are going to be the major causes for variation.
But you said the water vapour was due to evaporation, rather combustion which has equal importance as the production of CO2.
dv said:
Tamb said:
dv said:Like for like, CO2 is about twice as soluble in water. But we’re talking about much less than 1 part per thousand, still: the water is not going to dissolve enough oxygen or carbon dioxide to make an effect that is similar to the effect of the cooling.
I must be missing something. The water starts and finishes at the same temperature so cooling will make no difference because the water will return to it’s original temp.“The water starts and finishes at the same temperature”
The GAS is hot when you seal with the beaker. The GAS cools when the candle goes out.
The Rev Dodgson said:
dv said:
The Rev Dodgson said:You said that there would be about the same number of molecules in the air after combustion, which as far as I can see isn’t right at all.
I then mentioned carbon monoxide and water vapour, which are going to be the major causes for variation.
But you said the water vapour was due to evaporation, rather combustion which has equal importance as the production of CO2.
Fair dos, but (shrugs) the amount of water vapour in the gas that is right over a body of water is going to be determined by temperature (partial pressure of water is temperature dependant). If there is “excess” water vapour it is just going to enter the liquid phase.
dv said:
The Rev Dodgson said:
dv said:I then mentioned carbon monoxide and water vapour, which are going to be the major causes for variation.
But you said the water vapour was due to evaporation, rather combustion which has equal importance as the production of CO2.
Fair dos, but (shrugs) the amount of water vapour in the gas that is right over a body of water is going to be determined by temperature (partial pressure of water is temperature dependant). If there is “excess” water vapour it is just going to enter the liquid phase.
Well that’s the point isn’t it?
The combustion of 2 molecules of O2 produces one of CO2, and two of H2O. The H2O condenses, so the volume of the remaining CO2 is half the volume of the O2 (ignoring temperature change).
The Rev Dodgson said:
dv said:
The Rev Dodgson said:But you said the water vapour was due to evaporation, rather combustion which has equal importance as the production of CO2.
Fair dos, but (shrugs) the amount of water vapour in the gas that is right over a body of water is going to be determined by temperature (partial pressure of water is temperature dependant). If there is “excess” water vapour it is just going to enter the liquid phase.
Well that’s the point isn’t it?
The combustion of 2 molecules of O2 produces one of CO2, and two of H2O. The H2O condenses, so the volume of the remaining CO2 is half the volume of the O2 (ignoring temperature change).
Fair objections and I’d need to do some actual maths to compare this to the temperature effect, rather than just glibly stating it is negligible. I’ll be back.
dv said:
The Rev Dodgson said:
dv said:Fair dos, but (shrugs) the amount of water vapour in the gas that is right over a body of water is going to be determined by temperature (partial pressure of water is temperature dependant). If there is “excess” water vapour it is just going to enter the liquid phase.
Well that’s the point isn’t it?
The combustion of 2 molecules of O2 produces one of CO2, and two of H2O. The H2O condenses, so the volume of the remaining CO2 is half the volume of the O2 (ignoring temperature change).
Fair objections and I’d need to do some actual maths to compare this to the temperature effect, rather than just glibly stating it is negligible. I’ll be back.
Reinforces moll’s opening post, if nothing else :)
The Rev Dodgson said:
dv said:
The Rev Dodgson said:Well that’s the point isn’t it?
The combustion of 2 molecules of O2 produces one of CO2, and two of H2O. The H2O condenses, so the volume of the remaining CO2 is half the volume of the O2 (ignoring temperature change).
Fair objections and I’d need to do some actual maths to compare this to the temperature effect, rather than just glibly stating it is negligible. I’ll be back.
Reinforces moll’s opening post, if nothing else :)
Indeed.
dv said:
The Rev Dodgson said:
I’ve got what seems to be the correct answer, but I had to Binge to get it, so I won’t post it yet.I’d say it comes under the “should be bleedin’ obvious, but isn’t” category.
Also under the “why isn’t this better known” category.
Chastened by moll’s response, I took to Google as well.
Harvard University:Getting the facts right
When the oxygen is depleted, the candle goes out and the air cools. The volume of the air decreases and the water rises.Of course, it is possible the Internet and Me are both wrong, so I’ll be very interested in hearing the correct answer.
Yep. That’s the link that prompted this thread.
CH2 gives CO2 + H2O.
Uses up 1.5 molecules of O2, of which one hangs around as CO2 and the other condenses as H2O.
So the volume of air decreases by 1/3 of 21% of 100 mm = 7 mm.
Approximately, because there may (or may not) be other minor factors such as the temperature of air when the beaker is placed, the solution of CO2, the fraction of O2 remaining when the candle burns out, etc.
The Rev Dodgson said:
I’d say it comes under the “should be bleedin’ obvious, but isn’t” category.Also under the “why isn’t this better known” category.
Totally agree.
> Is CO2 more or less soluble in water than O2?
I would very much like to know that. It’s what made me look up that web link in the first place. Henry’s law applies. There’s a big difference in Henry’s law constant between O2 and CO2 but i don’t know if that means that CO2 is more soluble or less soluble.
“So the volume of air decreases by 1/3 of 21% of 100 mm = 7 mm.”
The water lift due to temperature change is typically 20 to 30 mm. It dominates any gas exchange effects.
Take a look at some vids.
https://www.youtube.com/watch?v=bBS_CacFY50
Nonetheless, it’s clear enough that the water-of-combustion is a significant effect, maybe 25% of the total, and I hadn’t thought of it before, so for that, I thank ye.
When you watch the videos, it gels. You see a trickle of water entering while the candle is burning, followed by a gush after the candle is extinguished.
dv said:
“So the volume of air decreases by 1/3 of 21% of 100 mm = 7 mm.”The water lift due to temperature change is typically 20 to 30 mm. It dominates any gas exchange effects.
Take a look at some vids.
https://www.youtube.com/watch?v=bBS_CacFY50
No no, you miss the point. The water lift due to temperature change is probably dominated by the condensation of water. Which is the gas exhange effect.
Another effect i haven’t considered is the effect of water pressure causing the air to expand, a little.
I wonder if it’s time to do some quantative experiments.
mollwollfumble said:
No no, you miss the point. The water lift due to temperature change is probably dominated by the condensation of water.
Nah, really, dog. You can even see it in the videos. Before the candle goes out, there’s a few millimeters of rise due to the gas exchange, then when it is extinguished, a few centimetres of rise due to the cooling.
You can eyeball the lift due to temperature change in those videos but if you want to make a from-first-principles ballpark: the flame of a candle is at 1400 C. A few centimetres away at the wall of the glass the air is ~150 C. It will be a bit hotter above the candle, somewhat cooler at the base near the water, but the average temperature in that glass is going to be at least 60 K above ambient. A 60 K drop down to room temperature is a 20% drop in volume at STP: that’s going to be quite a few centimetres for an ordinary beaker.
If someone walks into the room will that change the experiment?
dv said:
Nonetheless, it’s clear enough that the water-of-combustion is a significant effect, maybe 25% of the total, and I hadn’t thought of it before, so for that, I thank ye.When you watch the videos, it gels. You see a trickle of water entering while the candle is burning, followed by a gush after the candle is extinguished.
We need to define what we mean by “the cause of the gas volume reduction”.
If we are asking why there is a much greater volume reduction after the candle has gone out; that is almost entirely due to thermal effects; contraction on cooling, and condensation of water vapour on cooling.
If we are asking why there is an overall volume reduction, even though the air ends up warmer than when it started; since we can see from the videos that there is no escape of air from the container, even during the early stages of combustion, the overall volume change must be due entirely or almost entirely due to chemical effects.
“We” in this context means I, and you, dear reader.
Tau.Neutrino said:
If someone walks into the room will that change the experiment?
Why would it?
It’s possible the additional person might increase the air pressure by a very small amount, but it would be an immeasurable difference.
Unless none of the other people had been watching.
In that case you’d have a Schrodinger’s Candle experiment.
dv said:
mollwollfumble said:No no, you miss the point. The water lift due to temperature change is probably dominated by the condensation of water.
Nah, really, dog. You can even see it in the videos. Before the candle goes out, there’s a few millimeters of rise due to the gas exchange, then when it is extinguished, a few centimetres of rise due to the cooling.
Exactly, due to the condensation.
Interesting, but it’s not a simple experiment.
It’s dependent on the initial conditions.. What size flask, candle or how many candles, how hot do you get the air in the flask before lowering it, how fast.. Why googles but no other safely equipment? Why goggles at all ffs?Looks like it’s mainly about the cooling of hot air in the flask.
mollwollfumble said:
dv said:
mollwollfumble said:No no, you miss the point. The water lift due to temperature change is probably dominated by the condensation of water.
Nah, really, dog. You can even see it in the videos. Before the candle goes out, there’s a few millimeters of rise due to the gas exchange, then when it is extinguished, a few centimetres of rise due to the cooling.
Exactly, due to the condensation.
I’m not here.
On reflection, I think it must be almost entirely due to condensation, since the rate of cooling of a hot gas inside a glass would be much slower than shown in the videos.
That implies that the average temperature rise of the air must be much less than calculated by dv.
Would the experiment at different air temperatures and air pressures give different results?
Anyway, got distracted by these 7 AMAZING Physics Tricks That You Must See
The first one is nice to watch, the third one with the magnets needs a bit of your deductive reasoning applied to it.
Tau.Neutrino said:
Would the experiment at different air temperatures and air pressures give different results?
That’s affirmative
Ian said:
Tau.Neutrino said:
Would the experiment at different air temperatures and air pressures give different results?
That’s affirmative
Humidity levels as well.
Are they standards for experiment rooms in universities ?
Things like temperature, pressure, humidity, atmospheric cleanliness, radio frequency shielded.
Ways to speed up validation ?
Tau.Neutrino said:
Ian said:
Tau.Neutrino said:
Would the experiment at different air temperatures and air pressures give different results?
That’s affirmative
Humidity levels as well.
Are they standards for experiment rooms in universities ?
Things like temperature, pressure, humidity, atmospheric cleanliness, radio frequency shielded.
Ways to speed up validation ?
and each experiment room can be connected to other experiment rooms
left out
ratio of breathable gases in each room
Technically you’d need to allow for the fact that the candle is taking up part of the cross section at the base…
Also, note that only about 75% of the oxygen would be depleted. The candle won’t burn when the partial pressure of oxygen gets below 50 hPa or so.
The ratio of CO to CO2 in the products will be circa 1:25.
Also, the relative humidity in the air before the experiment could be anything, whereas afterwards it’s gonna be 100% in that beaker.
And also also, the oxygen will already be partly depleted in the region of candle already by the time the beaker comes down.
All of these will have second order effects.
The Rev Dodgson said:
dv said:
Nonetheless, it’s clear enough that the water-of-combustion is a significant effect, maybe 25% of the total, and I hadn’t thought of it before, so for that, I thank ye.When you watch the videos, it gels. You see a trickle of water entering while the candle is burning, followed by a gush after the candle is extinguished.
We need to define what we mean by “the cause of the gas volume reduction”.
If we are asking why there is a much greater volume reduction after the candle has gone out; that is almost entirely due to thermal effects; contraction on cooling, and condensation of water vapour on cooling.
If we are asking why there is an overall volume reduction, even though the air ends up warmer than when it started; since we can see from the videos that there is no escape of air from the container, even during the early stages of combustion, the overall volume change must be due entirely or almost entirely due to chemical effects.
“We” in this context means I, and you, dear reader.
Eh? The air doesn’t need to escape in order for the system to cool down.
dv said:
The Rev Dodgson said:
dv said:
Nonetheless, it’s clear enough that the water-of-combustion is a significant effect, maybe 25% of the total, and I hadn’t thought of it before, so for that, I thank ye.When you watch the videos, it gels. You see a trickle of water entering while the candle is burning, followed by a gush after the candle is extinguished.
We need to define what we mean by “the cause of the gas volume reduction”.
If we are asking why there is a much greater volume reduction after the candle has gone out; that is almost entirely due to thermal effects; contraction on cooling, and condensation of water vapour on cooling.
If we are asking why there is an overall volume reduction, even though the air ends up warmer than when it started; since we can see from the videos that there is no escape of air from the container, even during the early stages of combustion, the overall volume change must be due entirely or almost entirely due to chemical effects.
“We” in this context means I, and you, dear reader.
Eh? The air doesn’t need to escape in order for the system to cool down.
I was assuming that most of the heating of the air inside the glass would occur after the gap at the bottom was closed, which may or may not be correct.
Another variable to consider.
The Rev Dodgson said:
dv said:
The Rev Dodgson said:We need to define what we mean by “the cause of the gas volume reduction”.
If we are asking why there is a much greater volume reduction after the candle has gone out; that is almost entirely due to thermal effects; contraction on cooling, and condensation of water vapour on cooling.
If we are asking why there is an overall volume reduction, even though the air ends up warmer than when it started; since we can see from the videos that there is no escape of air from the container, even during the early stages of combustion, the overall volume change must be due entirely or almost entirely due to chemical effects.
“We” in this context means I, and you, dear reader.
Eh? The air doesn’t need to escape in order for the system to cool down.
I was assuming that most of the heating of the air inside the glass would occur after the gap at the bottom was closed, which may or may not be correct.
Another variable to consider.
Yes, the environment around the experiment has lots of variables.
The Rev Dodgson said:
dv said:
The Rev Dodgson said:We need to define what we mean by “the cause of the gas volume reduction”.
If we are asking why there is a much greater volume reduction after the candle has gone out; that is almost entirely due to thermal effects; contraction on cooling, and condensation of water vapour on cooling.
If we are asking why there is an overall volume reduction, even though the air ends up warmer than when it started; since we can see from the videos that there is no escape of air from the container, even during the early stages of combustion, the overall volume change must be due entirely or almost entirely due to chemical effects.
“We” in this context means I, and you, dear reader.
Eh? The air doesn’t need to escape in order for the system to cool down.
I was assuming that most of the heating of the air inside the glass would occur after the gap at the bottom was closed, which may or may not be correct.
Another variable to consider.
“I was assuming that most of the heating of the air inside the glass would occur after the gap at the bottom was closed, which may or may not be correct.”
Some. Dunno about most.
Tau.Neutrino said:
The Rev Dodgson said:
dv said:Eh? The air doesn’t need to escape in order for the system to cool down.
I was assuming that most of the heating of the air inside the glass would occur after the gap at the bottom was closed, which may or may not be correct.
Another variable to consider.
Yes, the environment around the experiment has lots of variables.
The external environment has lots of variables, but they all make very little difference, within the range of normal temp/pressure etc.
The experiment has been left overnight. This suggests that the system has had time to reach equilibrium, but I don’t know if overnight is sufficient time. Assuming that overnight is sufficient, then the water level inside the beaker will be the same as the water level outside. This is due to gas exchange through the water between inside the beaker and outside, driven by the gravitational potential of any water level difference.
KJW said:
The experiment has been left overnight. This suggests that the system has had time to reach equilibrium, but I don’t know if overnight is sufficient time. Assuming that overnight is sufficient, then the water level inside the beaker will be the same as the water level outside. This is due to gas exchange through the water between inside the beaker and outside, driven by the gravitational potential of any water level difference.
I can see there’s a need to really do this experiment. And variants to distinguish different effects. Eg. Different size candles.
mollwollfumble said:
KJW said:
The experiment has been left overnight. This suggests that the system has had time to reach equilibrium, but I don’t know if overnight is sufficient time. Assuming that overnight is sufficient, then the water level inside the beaker will be the same as the water level outside. This is due to gas exchange through the water between inside the beaker and outside, driven by the gravitational potential of any water level difference.I can see there’s a need to really do this experiment. And variants to distinguish different effects. Eg. Different size candles.
Going to try different waxes?
So in summary,
(1) it is not actually particularly simple an experiment, compared to, say, dropping the ball, and
(2) the stoichiometry of combustion accounts for almost the entirety of the effect, and the heating-and-cooling-condensing effect merely serves to counteract stoichiometric contraction while the candle is still alight, and
(3) we already all knew this?
Seems fair.
SCIENCE said:
So in summary,(1) it is not actually particularly simple an experiment, compared to, say, dropping the ball, and
(2) the stoichiometry of combustion accounts for almost the entirety of the effect, and the heating-and-cooling-condensing effect merely serves to counteract stoichiometric contraction while the candle is still alight, and
(3) we already all knew this?
Seems fair.
If you had asked me yesterday, I would have said yes.
If you ask me tomorrow, I might say yes.
But today I am saying no. As the glass is placed over the candle, the very hot air around the candle must displace some comparatively cool air from the glass, so at the time the seal is made the average temperature inside will be significantly greater than outside, and as the temperature drops after the candle goes out, this will contribute to the raising water level.
I don’t know how significant this is compared with the combustion effects, but (today) I would expect it to be non-negligible.
The Rev Dodgson said:
SCIENCE said:
So in summary,(1) it is not actually particularly simple an experiment, compared to, say, dropping the ball, and
(2) the stoichiometry of combustion accounts for almost the entirety of the effect, and the heating-and-cooling-condensing effect merely serves to counteract stoichiometric contraction while the candle is still alight, and
(3) we already all knew this?
Seems fair.
If you had asked me yesterday, I would have said yes.
If you ask me tomorrow, I might say yes.
But today I am saying no. As the glass is placed over the candle, the very hot air around the candle must displace some comparatively cool air from the glass, so at the time the seal is made the average temperature inside will be significantly greater than outside, and as the temperature drops after the candle goes out, this will contribute to the raising water level.
I don’t know how significant this is compared with the combustion effects, but (today) I would expect it to be non-negligible.
it’s equal to zero
i didn’t place any glass over any hot air, everything was glassed over already and i lit the candle remotely using electronic or photonic devices
(i didn’t actually but i could)
SCIENCE said:
The Rev Dodgson said:
SCIENCE said:
So in summary,(1) it is not actually particularly simple an experiment, compared to, say, dropping the ball, and
(2) the stoichiometry of combustion accounts for almost the entirety of the effect, and the heating-and-cooling-condensing effect merely serves to counteract stoichiometric contraction while the candle is still alight, and
(3) we already all knew this?
Seems fair.
If you had asked me yesterday, I would have said yes.
If you ask me tomorrow, I might say yes.
But today I am saying no. As the glass is placed over the candle, the very hot air around the candle must displace some comparatively cool air from the glass, so at the time the seal is made the average temperature inside will be significantly greater than outside, and as the temperature drops after the candle goes out, this will contribute to the raising water level.
I don’t know how significant this is compared with the combustion effects, but (today) I would expect it to be non-negligible.
it’s equal to zero
i didn’t place any glass over any hot air, everything was glassed over already and i lit the candle remotely using electronic or photonic devices
(i didn’t actually but i could)
I was talking about the experiments as done in the videos dv posted. Yes you could do it by lighting the candle after placing the glass.
Let us know how much difference that makes.
dv said:
The Rev Dodgson said:
I’ve got what seems to be the correct answer, but I had to Binge to get it, so I won’t post it yet.I’d say it comes under the “should be bleedin’ obvious, but isn’t” category.
Also under the “why isn’t this better known” category.
Chastened by moll’s response, I took to Google as well.
Harvard University:Getting the facts right
When the oxygen is depleted, the candle goes out and the air cools. The volume of the air decreases and the water rises.Of course, it is possible the Internet and Me are both wrong, so I’ll be very interested in hearing the correct answer.
Internet is definitely wrong. I just did the experiment (short term not overnight) with a tealight candle in an olive jar and the rise in water level was 14±2%.
Web link’s condensation of water vapour can only give 7%.
So it looks like air cooling plays a very big role.
mollwollfumble said:
dv said:
The Rev Dodgson said:
I’ve got what seems to be the correct answer, but I had to Binge to get it, so I won’t post it yet.I’d say it comes under the “should be bleedin’ obvious, but isn’t” category.
Also under the “why isn’t this better known” category.
Chastened by moll’s response, I took to Google as well.
Harvard University:Getting the facts right
When the oxygen is depleted, the candle goes out and the air cools. The volume of the air decreases and the water rises.Of course, it is possible the Internet and Me are both wrong, so I’ll be very interested in hearing the correct answer.
Internet is definitely wrong. I just did the experiment (short term not overnight) with a tealight candle in an olive jar and the rise in water level was 14±2%.
Web link’s condensation of water vapour can only give 7%.
So it looks like air cooling plays a very big role.
10%, not 7%.
2 O2 molecules turn into 1 CO2 and 2 H2O, so gas volume reduced by half (after condensation) x % O2.
Are you people saying % instead of mm or do you mean %?