Internal energy and expanding gas

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SUMMARY

The discussion centers on the thermodynamic principles governing an expanding gas, specifically the calculation of internal energy change (ΔU) and volume change under constant pressure conditions. The user correctly applies the first law of thermodynamics, ΔU = Q - W, where Q is the heat absorbed (17x10^5 joules) and W is the work done by the gas (8x10^5 joules). The user also contemplates the use of the equation PΔV = Q - ΔU, noting that it is unnecessary since work is provided directly.

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  • Understanding of the first law of thermodynamics
  • Familiarity with concepts of internal energy and work
  • Knowledge of gas laws, particularly under constant pressure
  • Basic algebra for manipulating equations
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tomahawk1985
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17x10^5 joules are absorbed by an expanding gas that does 8x10^5 joules of work. (a) Find ΔU; (b) Assuming it expands at constant pressure, what's the change in volume?

Am I correct to use this:

ΔU = Q - W

Then after finding ΔU,

PΔV = Q - ΔU

Or does this make no sense?
 
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Both equations are OK. Except the second one is not really required, since you are given W directly.
 

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