A 100cm^3 box (1X10^-4 m^3) contains helium at a pressure of 2.0 atm and at a temperature of 100C (373K) It is placed in thermal contact with a 200cm^3 (2x10^-4 m^3) box containing argon at a pressure of 4.0atm and a temp. of 400C (673K)(adsbygoogle = window.adsbygoogle || []).push({});

a) What is the initial thermal energy of each gas?

b) final thermal energy?

c)How much heat is transferred?

d)Final Temp?

e)Final pressure of each?

OK, I got part a).

First I used [tex] PV = nRT [/tex] to solve for the mols of each gas. Then I used

[tex] E_{th} = 3/2nRT[/tex]

to find the thermal energy of each gas.

Helium- .007mol, 30.4 J

Argon- .0145 mol, 121.6J

These answers for the initial thermal energy are right. My problem starts in part B.

To find the thermal energy of gas A you'd use the formula:

[tex] E_A = \frac{n_A}{n_A+n_B}E_{total} [/tex]

When I use this formula to find the final thermal energy of Helium I get:

[tex] E_{He} = \frac{n_{He}}{n_{He}+n_{Ar}}E_{total} [/tex]

[tex] \frac{.007}{.0215}(152J) = 49.5 J [/tex]

That would also give me 102.5 J for Argon. Both of these final thermal energies are wrong according to the book but I can't see my mistake. Because of this I get part c, d, and e wrong also. Can someone help me out here? Thanks.

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# Homework Help: Initial and Final Thermal Energies of a Gas

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