Help with Physics please

is maith liom chocolate

Can anyone give me an answer for this, I got 2.15*10^-5, but I'm not really sure it's correct. Please help.


A glass bulb of volume 400 cm^3
is connected to another of volume 200 cm^3
by a tube of
negligible volume. Both bulbs initially contain dry air at 20^oC and 1 atm. The larger bulb
is then immersed in steam at 100^oC and the smaller in melting ice at 0^oC. Find the
common pressure in the system.

Morbert

is maith liom chocolate wrote: »

Can anyone give me an answer for this, I got 2.15*10^-5, but I'm not really sure it's correct. Please help.


A glass bulb of volume 400 cm^3
is connected to another of volume 200 cm^3
by a tube of
negligible volume. Both bulbs initially contain dry air at 20^oC and 1 atm. The larger bulb
is then immersed in steam at 100^oC and the smaller in melting ice at 0^oC. Find the
common pressure in the system.

You need to specify units. 2.15*10^-5 what? atms? Pascals?

The law you should consider is P V = m R T

The steps you should follow are:

1. Find the mass of the air in the bulb. The total mass is

m1 + m2 =
(400cm^3 * 1 atm ) / (R * 293 K) +
(200cm^3 * 1 atm ) / (R * 293 K)
= M

Note the Temperature is in Kelvin (0 C = 273 K)

2. The mass in the bulb will be conserved even when the temperature difference is introduced. I.e. We have the relation

M =
(400cm^3 * P ) / (R * 373 K ) +
(200cm^3 * P ) / (R * 273 K )

The only unknown above is P. Solve for P.

is maith liom chocolate

Oh that makes so much more sense than what I was doing. I was trying to use PV=NkT as that's the equation we were taught in our Physics lectures. I've never seen that version of the equation though, PV=mRT

If I were to use PV=NkT, would it make it more complicated?

Thank you so much for your help. It's my first year doing Physics and even little things are starting to confuse me now

Morbert

is maith liom chocolate wrote: »

Oh that makes so much more sense than what I was doing. I was trying to use PV=NkT as that's the equation we were taught in our Physics lectures. I've never seen that version of the equation though, PV=mRT

If I were to use PV=NkT, would it make it more complicated?

Thank you so much for your help. It's my first year doing Physics and even little things are starting to confuse me now

Yes, you can use PV = NkT either. They are describing the same phenomena.

1.
n1 + n2 =
(400cm^3 * 1 atm ) / (k * 293 K) +
(200cm^3 * 1 atm ) / (k * 293 K)
= N

2.
N =
(400cm^3 * P ) / (k * 373 K ) +
(200cm^3 * P ) / (k * 273 K )

is maith liom chocolate

oh right, thanks a million, you were such a help!

Couldn't for the life of me figure it out. thanks again