physics question

[UCBPride]

if 9g of water is placed into a 2L pressure cooker and heated to 500c, what is the pressure inside the container?

PV=nRT, but how do i get n??

n=m/M (mass / mole)

or should i ask, how do i get the molar mass? wtf is molar mass anyway


sigh, i wish i was smart

 

[OS]

<< wtf is molar mass anyway >>



Molar mass is how much one mole of the given molecule weighs.

 

[notfred]

water = H20

molar mass of water is like 18 (roughly)

Add up the atomic weight of the 2 hydrogens and the oxygen. That number in grams is your weight/mole of water.



*Disclaimer - it's been several years since I took chemistry. and this is a chemistry question, not physics (at least where I went to school)

 

[jamesave]

H2O : 1+1+16 = 18 the molar mass of water

EDIT:

notfred, you beat me!

 

[Rakkis]

once you have your molar mass (i.e. ~ 18 grams/mole)

you multiply your mass (9g) times (1 mole/ 18 grams) and you get n=0.5 mole.

 

[Ameesh]

<< sigh, i wish i was smart >>




your not dumb just lazy, you could have easily look up what molar mass is.

 

[UCBPride]

wow you guys rock

heres another question for ya. what am i doing wrong here: P= nRT/ v where R = .0821, T=773.15 K, n=.5, V = 2 comes out to 15.8 but the answer is 16.1

 

[jamesave]

Make sure all the units are correct! Especially the R value..

 

[monto]

i tried using the slightly more exact R value of 0.8206, but nada, also tried O and H molecular mass at 6 significant digits, but still nada, so i'm guessing the difference in the answer is due to something perhaps in the instructions, ie are you to assume all 9g of water is turned into water vapor, are you to assume the water vapor is an ideal gas? (cause realistically it's far from)...worse comes to worse, just round your answer to 16atm

btw, is this physics 8A?

 

[jamesave]

If you're not assuming it's ideal, then it's PV=nRTz where z is the compression factor..


EDIT: The sentence above maybe wrong. Since this is water vapor, you may need to llok at super steam chart..