## Wednesday, October 27, 2010

### Woops, forgot to post this... Oct 25th Lecture

Oct 25th 2010

Starting off today's lecture filled with hot air.  Or rather, hot Nitrogen.

Air Bag Chemistry:

2NaN3(s) -> 2Na(s) + 3N2(g)

Calculate the volume of Nitrogen gas produced if the temperature is 80 degrees C, and the pressure is 823mmHg.  60g of NaN3 is ignited.

Its a straight ideal gas problem, use the equation V = (nRT)/P
Where n is moles of stuff, R is the gas constant, 0.082(L*atm)/(mol*K), T is temperature (in Kelvin), and P is pressure in atm.

Ha.. ha... so we're watching the same movie about the same scuba divers again...

So the reason we rewatched that was:

Why are scuba tanks pressurized with excess helium?

Turns out that the pressure of Oxygen in the normal atmosphere is only about 0.2atm compared to the total of 1atm, so the tank needs to have only 20% oxygen by pressure, so they add helium to create that other 80% of the pressure needed.

After talking some more about the group of people working on redefining the kilogram, we're on to the next chapter, Thermochemistry.  So this will deal with energy a lot.

Unit of energy is the Joule

Hmm... I'd almost say I missed a bunch of something rather because everybody is leaving... but by the looks of the slides, he just talked about heat a little... then class is over... so this post is over!