Thermodynamics- energy, pressure, volume

AI Thread Summary
The discussion revolves around solving a thermodynamics problem involving internal energy, heat absorption, and work done at constant pressure. The internal energy increases by 1350J when the system absorbs 1150J of heat energy, leading to confusion about calculating the work done on the system. Participants clarify that the first law of thermodynamics (U = q + w) should be applied, where U is the change in internal energy, q is the heat absorbed, and w is the work done. The correct calculation reveals that the work done is 200J, allowing for the determination of the volume change, which should be 2E-3 m^3. Understanding these relationships is crucial for solving similar thermodynamic problems effectively.
name_ask17
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Homework Statement


The internal energy of a system increases by 1350J when the system absorbs 1150J of heat energy at a constant pressure of 1.01E5 Pa. By how much does the volume of the system change?


Homework Equations


Im not sure how to approach this but would i use the isobaric equation since the pressure is constant?
w=-P(change in V)


The Attempt at a Solution


I attempted to take the change in the work (1350) and divide out pressure, but that did not give me the correct answer.
(The answer should be 2E-3m^3, but i just don't know how to get there)
 
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name_ask17 said:
I attempted to take the change in the work (1350)
That's not the work done on the system. (That's the total change in internal energy.)

(But your method is exactly right. Just find the correct value for the work and you'll be fine.)
 
Last edited:
Doc Al said:
That's not the work done on the system. (That's the total change in internal energy.)

(But your method is exactly right. Just find the correct value for the work and you'll be fine.)

But I am still confused on what i am supposed to use for work
 
name_ask17 said:
But I am still confused on what i am supposed to use for work
What does the 1st law of thermo tell you?
 
U=q+w
 
is that correct? and is so, how do i use that in this problem? i am confused.
 
name_ask17 said:
U=q+w
Exactly. You're given U and q, so what's w?
 
the answer to this problem should be 2E-3 but i can't seem to get that
 
i just add them? but then i get the answr of .023. and that's not right
 
  • #10
name_ask17 said:
i just add them?
Add what?

U = ?
Q = ?

Solve for W.
 
  • #11
can you explain to me what i am doing wrong?
 
  • #12
which one is U? would it be the 1350?
 
  • #13
or would that be the q?
 
  • #14
name_ask17 said:
which one is U? would it be the 1350?
Yes, U = change in internal energy.
 
  • #15
so does that make the w 200?
 
  • #16
name_ask17 said:
so does that make the w 200?
Yes.
 
  • #17
thank you!
 

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