Question about light gasses.

Beyond curious.

Hi, call me stupid or whatever but here is something that is puzzling me for some time now.
What will be the heaviest,[1] a bottle full of a very light gas like hydrogen or helium, [2]this same bottle but with the hydrogen replaced with air or [3] the same bottle but with nothing [vacuum] in it? Thanks.

AlienGav

Before taking this into consideration, you must realise that Air is a mixture of gases.

If all the bottles are the same size, example 1ltr (and their temprature and pressure is the same) ,then their volumes are all the same. It's important to differentiate the difference between Mass and Volume. Mass is the amount of matter in an object. (It can never change, unlike something's weight which can change quite easily due to gravity and pressure etc.)

Anyways......

Every molecule of all of the above gases have different masses.

For instance,
A 1ltr bottle filled with a light gass like Helium, would have a smaller mass than a 1ltr bottle filled with air.

Air is a mixture of heavier gasses, Namely Nitrogen 78%, Oxegen 21%, and Carbon dioxide etc... Collectively, the differnet gases found in the Mixture of air have a greater mass than that of the Litre of Helium.

And lastly, the bottle which has been vacumed would be the lightest of the three, as it contains no matter whatsoever on the inside. (No matter = No mass)

Hope u can understand my crazy explanations!

Beyond curious.

Thank you very much for your reply, your explanation is quite understandable.

EamonnKeane

If all the bottles are the same size, example 1ltr (and their temprature and pressure is the same) ,then their volumes are all the same.

Even if their pressures were different, the gas samples would still have the same volume because they're both in containers of 1 L capacity.

It's important to differentiate the difference between Mass and Volume. Mass is the amount of matter in an object. (It can never change, unlike something's weight which can change quite easily due to gravity and pressure etc.)

Scientifically, weight isn't actually a prperty of an object: it's defined as "the interaction of matter with a gravitational field". Increasing/decreasing the gravitational field will change its weight, but changing the pressure acting on it will make no difference.

Capt'n Midnight

http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/idegas.html

the volume of a gas depends on temperature, pressure and the number of molecules (or atoms for monatomic gasses) so under atmospheric conditions the weight of a given volume of gas is proportional to it's molecular weight

For Hydrogen H2 the molecular weight is 2

2 grammes of it has 6.0221 x 10^23 molecules of gas
and at 0 degrees C it has a volume of 22.4 liters

Uranium Hexafluoride (are there heavier gases at room temp ?)
molecular weight is 349 or 352, corresponding to U-235 or U-238
so 6.0221 x 10^23 molecules of gas weigh 352 grammes and have a volume of 22.4 litres at 0 degrees. So it's 176 times heavier than Hydrogen.

Very roughly a cubic meter of air weighs 1Kg

Capt'n Midnight

http://en.wikipedia.org/wiki/Lighter_than_air

Also heard somewhere of an idea to use an inner ballon of Hydrogen for lift but surrounded by Ammonia to stop it catching fire. Another idea was airships using a mix of Hydrogen , Methane and other flamable gases for fuel in a mix that was the same density as air so you would not have to adjust the trim or buoyancy during flight.

Panserborn

Is it Boyles law that states that 1 mole of any gas occupies 22.4L? Was Boyle Irish?

Capt'n Midnight

http://en.wikipedia.org/wiki/Robert_Boyle

EamonnKeane

No Boyle's law was that pressure in a gas is proportional to volume