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Year 2 Chemistry Degree Q (Thermodynamics)

Hey,

this is actually a Q to help with recap of Year 1 Thermodynamics (it's obvious I learnt it well...) hope someone can answer my Q!

- A system consisting of 1.5 mol of CO2(g) initially at 288.15K and 9atm (101325pa x 9) & confined to a cylinder of cross section 100cm2

- The sample is then allowed to expand adiabatically against an external pressure of 1.5 atm until the poston has moved outwards through 15 cm, assume that CO2 is a perfect gas with Cv,m = 28.8 J/K/mol

calculate q, w, deltaU, deltaT & deltaS...

Now I know that adiabatically, there is no heat exchange, therefore q = 0, which means w = deltaU. I know i'm given the hint of a 'perfect gas' so should I be implementing PV = nRT?

Much appreciated guys, been doing organic chemistry non-stop, when it gets to physical... my brains just dead!

Thanks in advance!

(edited 12 years ago)

Reply 1

shengoc

yeah you are on the right track.
q = 0
dU = dq + dw = dw

dU = -p dV

assume ideality

dU = - nRT/V dV

The key is that in the piston, volume = cross section x length

so you are supposed to work out volume from the dimensions given above.

it is adiabatic, as no heat is lost or gained, but there is gas expansion, work is done, so temperature must change.
all these is in atkins.