Need help for a homework

[roll]

[Crimson Wizard]

Umm... I usually fail chemistry. But in terms of physics, you should know each gas's density to calculate that.

EDIT: Hmm, or maybe not.
Basically speaking, pressure = something like M * (height level) / T, where M is molar mass and T is temperature. since I guess height and temperature may be considered equal, you need to know their molar masses, and compare them

not sure I do not miss something though. Didn't have such "puzzles" for many years.

Then again, why not just google it?

[Snake]

If I honestly tried to figure that out, my answers would still amount to...

[Joseph DiPerla]

 :o

I knew I should have paid attention in school.

[Lufia]

P*V = N*R*T

That was like, the only thing to remember when dealing with gases, no?

P = pressure
V = volume
N = number of molesare = the gas constant
R = gas constant
T = temperature

Given that v,are and t are equal, the gas with the highest pressure is the one with more moles. To find that, you use the molar mass of the atoms and the mass given in the exercise, and do a division.

Something along these lines, at any rate. It's been a while since I last did physics / chemistry.

Edit : The hell ? And if I want to write "r" ? Well, capital letters it is, then.

[arj0n]

Doesn't the answer depend on the temperature of the bottles and the gas?

[roll]

Temperature has nothing to do in this. Humm I am gonna give a try:

N² = 28,01grams/1mol
CO² = 44.01grams/1mol

28,01g    10g
--------- = ------       ? mol = 0.36mol
1 mol       ?mol       

44.01g     12g
--------- = ------      ? mol = 0.27mol
1 mol       ?mol


So ok, N² has more moles (more particules)... But 12 grams is more then 10 grams, and mass also influes the pressure... What should I do now?

[Babar]

n=mass/molar mass.

Temperature and volume would probably be the same for both bottles/gases, and R is a constant, so

whichever has the greater (mass/molar mass) will have the greater pressure.

[ThreeOhFour]

I like how it is specified that the glass bottles are made out of glass. I guess it's good to make sure we know...

[Scarab]

Okay,

PV=nRT

therefore
P= (nRT)/V

as T and V are constant, P α nR (α meaning "is proportionate to")

as R is a constant (8.315 J K^-1 Mol^-1)

P α n.


Now we have to work out n.


n(CO₂)= mass/(Molar Mass) = 15/(12.01+2(16.00))** = 0.2830 mol.

n(N₂)= m/M = 10/(2(14.01))** = 0.5549 mol.

as n(N₂) > n(CO₂)

    P(N₂) > P(CO₂)


** Molar mass values taken from chemistry data sheet

So ok, N² has more moles (more particles)... But 12 grams is more then 10 grams, and mass also influes the pressure... What should I do now?

The only thing that mass influences is the number of moles. (as m= nM)
As the mass of each particle is constant, more particle means more mass, and vice-versa.

Hope this helps
Peace
Scarab

[Ali]

You guys with the formulae seem to have missed the point.

There's obviously more pressure for CO2. With CO2 everyone's all, "Keep that tree alive! Stop killing the planet!"

Nitrogen gets it pretty easy, all it has to keep alive are the aliens from Mars Attacks, which is pretty much Tim Burton's worst film.

Please post any gold stars you recieve using my answer in this thread so that I can add them to my scrap book.

[Andail]

Here's one, feel free to include it in your signature.

[Haddas]

It would be cool to have a dedicated thread for solving physics/maths/chemistry problems. Although I do not think that's in too much demand really.

[Shane 'ProgZmax' Stevens]

Here you go, Ali.  I cleaned up Andail's gold star for you and I even made it forum signature friendly!

[Scarab]

It would be cool to have a dedicated thread for solving physics/maths/chemistry problems. Although I do not think that's in too much demand really.

Have at ye!


A watch has a minute hand that is 8mm long and a second hand 10 mm long.



(a) Determine the angular speeds of rotation of the minute and seconds hands in radians per hour.

[2]

(b) If the angle between the minute and seconds hands is θ, and the distance in millimetres between the tips of these hands is x, show using the cosine rule that x² = 164 - 160 cosθ.

[2]

(c) At exactly 7.20pm, how fast is the distance between the tips of the hands chcnging? Give your answer in mm/s correct to 2 decimal places.

[6]

Have fun!
Peace
Scarab

[Ali]

Thanks for the stars guys! I'm obviously pretty great at physics.

The first person to answer Scarab's question correctly wins my much coveted gold star!

[Khris]

EDIT: Please disregard the horribly wrong mess I've posted below...

a)

as_m =  120π
as_s = 7200π

b)

x² = 8² + 10² - 2*8*10 cosθ

x² = 164 - 160 cosθ

c)

x = (164-160cosθ)^0.5
dx = 0.5*(164-160*1)^-0.5
dx = 0.5*4^-0.5
dx = 1/2 * 1/(4^0.5)
dx = 1/(2*2)

dx = 0.25



A faucet takes 20 minutes to fill a bathtub.
The drain empties it in 50 minutes.

How long does it take to fill the bathtub if the drain isn't plugged?

[Bulbapuck]

Vol = v1*20
Vol = v2*50
v3 = v1 - v2 = Vol/20 - Vol/50 = Vol*(3/100)
Vol = v3 * (100/3)

Ans: 100/3 mins

The answer is not exactly pretty, did I do something wrong? EDIT: yes I did, now?


A man is shot out of a cannon with a velocity of 10 m/s, 20 m straight forward (at the same level as where he's shot out of the cannon) is a safety net. Will he make it?

[Khris]

100/3 is correct, I chose arbitrary numbers.

Re your question: what's the cannon's angle? Also straight? Then no, because gravity will move him below the net.

[Bulbapuck]

100/3 is correct, I chose arbitrary numbers.

Re your question: what's the cannon's angle? Also straight? Then no, because gravity will move him below the net.

I never said the cannon's angle was straight. It might be gay for all I know
And it could also very well have an angle, it's just not mensioned in the question as to wether or not it does.
Let me put it this way: is it possible?