Change in internal energy for an isobaric process?

  • #1
Question:

When a quantity of monatomic ideal gas expands at a constant pressure of [tex]4.00 \times 10^{4} {\rm Pa}[/tex], the volume of the gas increases from [tex]2.00 \times 10^{ - 3} {\rm m}^{3}[/tex] to [tex]8.00 \times 10^{ - 3} {\rm m}^{3}[/tex].

A.

What is the change in the internal energy of the gas?

It's isobaric, so the pressure is constant.

I know the work is [tex]P\Delta V = (4.00 * 10^4)(6.00 * 10^{-3})[/tex].

But, I don't know how to get [tex]\Delta U[/tex] from this.
 
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Answers and Replies

  • #2
Physics Monkey
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What variables does the internal energy of the ideal gas depend on? How do these variables change in the aforementioned process?
 
  • #3
OK, the internal energy depends only on temperature.

For a monatomic gas, [tex]\Delta U = \frac{3}{2}nR\Delta T[/tex].

I don't know the number of moles or the change in temperature.
 
  • #4
Physics Monkey
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Progress! Ok, so now you need to know the change in temperature times [tex] n R [/tex], right? You know the pressure and volume of the gas at two different points in P,V space. Can you use this information to find the unknown? Hint: ideal gas law.
 
  • #5
mezarashi
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This relationship should be helpful as well.

[tex]\Delta U = Q - W [/tex]

Apparently you have the equation for the W right. Now use the ideal gas law and a bit of calorimetry.
 
  • #6
Thanks a lot!
 

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