do you know science?

[Lasse Langwadt Christensen]

"Scorn and derision"? Check out Phil Allison for what you've got to produce for a Sydney audience to register scorn or derision.

I stumbled in this and immediately thought of Phil (and a few others)
colorful language

-Lasse

 

[RichD]

As another muddy point, the article discusses
the temperature drop, as the expelled gas
expands into some volume. In the example
given, air escapes into the atmosphere. How
does one measure the 'expansion', how do you
even define it?

 

[Bill Sloman]

That's a new one on me, I don't keep up with the
latest chemistry research.

James Prescott Joule died in 1889. William Thompson - Lord Kelvin - hung around to 1907. The work was done in 1852, 160 years ago.

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

http://en.wikipedia.org/wiki/William_Thomson,_1st_Baron_Kelvin

The work was in thermodynamics, which is physics, rather than chemistry (though you will get taught about it if you study chemistry at university. I got taught about in my second year, in 1961. There's been quite a lot of stuff discovered since then.

But anyhow, that effect refers to the gas
EXTERIOR to the container. The question
here involves the gas remaining inside.

The thermodynamics covers that too.

Though the Wikipedia article is poorly written,
typical of that site. Which means you cited
an incomprehensible reference, one which YOU
uncomprehend.

That second year course on thermodynamics took me quite a while to comprehend, but I did get my head around it. Thermodynamics is notoriously difficult to teach. The wikipedia article struck me as a well-written popularisation, but it's always difficult to gauge the quality of material that is teaching people stuff you already understand.

The quiz is motivated by the ideal gas law.
I always thought, one equation, multiple
degrees of freedom, how the heck can you
determine anything?

So with this pressurized water bottle,
if we examine the formula:

pv = nRT

That's only true for an ideal gas. The Joule-Thompson effect varies betweengases, so it isn't covered by the ideal gas equation. In fact what's goingon is that the van de Waals forces between the gas molecules (which decrease as the 6th power of molecular separation) decrease as the gas expands, and this slows down the average speed of the gas molecules (which means thatthey are cooler) - for everything except hydrogen, helium and neon at roomtemperature. There's another effect which works the other way (as spelled out on the web-site) but it's smaller for your pressurised bottle of wet air at room temperature.

<snip>

 

[Bill Sloman]

If you fill a canvas bag with water, the water slowly wicks to the outside, where it evaporates, this cools the rest of the water inside. Not sure what they are called, but I say them in Australia many moons ago. (I guessthey work best in a dry climate.)

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

 

[George Herold]

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

Excellent, Thanks, me mum's from Perth in WA.

They hung 'em on the 'roo bars of their trucks.
('roo is short for kangaroo, which fill the same niche as deer in the US.)

George H.

 

[[email protected]]

Hi Rich, So if you take two bottles, one full of gas and the other empty.
And then you connect them and let the gas flow from one to other, then the gas filled bottle gets cold and the bottle that started empty gets hot. And if you take both bottles as the whole system, then it looks like thermo predicts that the temperature of the total system doesn't change. It seems like the exact temperature difference will depend on how the gas is transfered.... after all I could always let the gas spin some generator and get energy out of the system.

That assumes no friction in the nozzles/pipe or other losses. If you
include the universe as the "system", then there is no energy lost,
either. ;-)