[cofi]

1. A sample of carbon dioxide of mass 2,45g at 27°C is allowed to expand reversibly and adiabatically from 500 cm³ to 3.00 dm³. What is the work done by the gas?

2. A sample of 4.0 mol O₂ is originally confined in 20 dm³ at 270 K and then undergoes adiabatic expansion against a constant pressure of 600 Torr until the volume has increased by a factor of 3.0. Calculate q, w, deltaT, deltaU and deltaH. (The final pressure of the gas is not necessarily 600 Torr.)


I've been trying to solve these problems for about 2 hours... I just can't find the right formula to start with...

[Hunt]

In this case dU = -dW

Remember that for an adiabatic process,? T₁V₁^{(gamma - 1)} = T₂V₂^{(gamma - 1)}

You can determine the final temp from here ( I think gamma for CO2 is given in your thermodynamics book ), and then find dU.

[plu]

In this case dU = -dW

I believe this should be dU = dW.  Then, a decrease in temperature would result in a negative sign for work, indicating work being done by the system through expansion.

[Hunt]

dU = -dW is correct taking into consideration the work done by the gas on the surr.

dW_int = - dW_ext

dW_ext = - PdV , dW_int = PdV

( this can be proven using vectors )

dU = -dW_int + dq ---> dU = - dW_int = - PdV

dU = dW_ext +dq ---> dU = dW_ext = - PdV

The expression of dU depends on how u define the work ... but it's the same value.

[Donaldson Tan]

cofi: what data are you provided?