A Level Physics Help

decmatt · 31 Dec 2007 at 16:48

Hi,

Just revising for my resits and think I must have lost my notes on this bit, I have no idea what to do so can someone just try and explain things please.

1)a) A balloon contains 0.40 mol of helium at 300K. Calculate

i) the number of helium atoms in the balloon
ii) the kinetic energy of a helium atom in the balloon
iii) the total kinetic energy of the helium atoms in the balloon

Can anyone try and explain things pleae.

Many Thanks

crowhorse · 31 Dec 2007 at 16:52

Solac said:
Hi,

Just revising for my resits and think I must have lost my notes on this bit, I have no idea what to do so can someone just try and explain things please.

1)a) A balloon contains 0.40 mol of helium at 300K. Calculate

i) the number of helium atoms in the balloon
ii) the kinetic energy of a helium atom in the balloon
iii) the total kinetic energy of the helium atoms in the balloon

Can anyone try and explain things pleae.

Many Thanks

i - 1 mol of a gas at standard temp & pressure takes up 24 litres, so no. of helium atoms = (0.40/24)*avogadro's number

Tefal · 31 Dec 2007 at 16:52

ooo i remeber this,

i)You need avogadro's constant,

ii)and you'll need to know how to work out root mean speed iirc (think that's it)

other wise get your text book and look up the gas equations.

Tefal · 31 Dec 2007 at 16:53

crowhorse said:
i - 1 mol of a gas at standard temp & pressure takes up 24 litres, so no. of helium atoms = (0.40/24)*avogadro's number

no its just 0.4 * avogadros constant.

Gaverick · 31 Dec 2007 at 16:54

i) 6.02 × 10^23 (avogadro constant) x 0.4 = 2.408^23

I think

Fusion · 31 Dec 2007 at 16:57

i) A mol, or mole, contains Avogadro's number (approximately 6.022×10^23) of entities.

ii) Kinetic energy of an atom is described by 3/2kT, where K is Boltzmann's constant (1.3806503 × 10^(-23)). T is the temperature of the substance in Kelvin.

iii) Multiply your answer for part ii) by the number of atoms in the baloon.

Cold_And_Miserable · 31 Dec 2007 at 16:58

i)0.4A= ...x10^23 atoms
ii) not possible due to uncertainty
iii) heat capacity of helium per mole x 0.4 x 300 = ?

crowhorse · 31 Dec 2007 at 16:59

Tefal said:
no its just 0.4 * avogadros constant.

shhhhh

Amleto · 31 Dec 2007 at 17:01

beaten like like a things that gets beaten.

gumbald · 31 Dec 2007 at 17:05

My contribution was going to say it's something to do with Avagadro. A-Level physics is getting too long ago to remember

Aod · 31 Dec 2007 at 18:06

this is AS physics right? we didn't have AS exams in january when i did it...

Visage · 31 Dec 2007 at 18:24

PanMaster said:
ii) not possible due to uncertainty

Wrong. Its a statistical mechanics question; The equipartition theorem states that each atom has, on average, 1/2 kt Joules of energy per degree of freedom. In this case hgere are 3, so the average energy is 3/2 kt, as stated previously.

prUnE · 31 Dec 2007 at 18:44

Aod said:
this is AS physics right? we didn't have AS exams in january when i did it...

I've got my Module 1 exam next friday! :eek:

It's differs with which school you go to.

Spitfir3 · 31 Dec 2007 at 18:45

I did this yesterday revising ^^

2.) KINETIC ENERGY = 2/3 kT = k being the boltzmans constant
3.) part 1 X part 2

edit. explanation.. shulda got a revision guide

Aod · 31 Dec 2007 at 18:50

prUnE said:
I've got my Module 1 exam next friday!
It's differs with which school you go to.

Good luck matey. remember, A2 physics is actually easier!

anyway, after your exams you can safely forget everything. as long as you did well, that is!

Amleto · 31 Dec 2007 at 21:46

Spitfir3 said:
I did this yesterday revising ^^

2.) KINETIC ENERGY = 2/3 kT = k being the boltzmans constant
3.) part 1 X part 2

edit. explanation.. shulda got a revision guide

revise again. 3/2 kT isnt it?