First law of thermodynamics applied to Compression and Expansion

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The first law of thermodynamics indicates that during the compression or expansion of a gas at constant temperature, the change in internal energy (ΔU) is zero for an ideal gas. This implies that any heat added or removed from the system (ΔQ) must balance the work done on or by the system (W). While compression at constant temperature typically suggests heat is extracted, it is crucial to recognize that ΔQ is not zero. The discussion emphasizes that these principles are based on experimental observations and mathematical formulations applicable to ideal gases. Understanding these concepts is essential for grasping the behavior of gases under varying conditions.
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How does the first law of thermodynamics apply to the Compression And expansion of a gas at constant temperature ?

If the gas is at a constant temperature and is being compressed, then
ΔQ = 0
ΔU = +
W(on the system) = +


Are those(^^) correct ?

The equation being :
ΔU = ΔQ + W(on the system)
 
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Compression or expansion at constant temperature means heat is extracted or added.
 
At constant temperature ΔQ is not zero. ΔU is zero, for ideal gas.
 
nasu said:
At constant temperature ΔQ is not zero. ΔU is zero, for ideal gas.

would u explain "why" ?
 
would u explain "why" ?

Originally this was an experimental fact about gasses. Nowadays there is maths to back it up, and we know that it only applies to ideal or perfect gasses.




http://demonstrations.wolfram.com/JouleExperimentOnFreeExpansion/

If you can cope with the maths google has lots on the Joule experiment and the Joule-Thompson experiment.

If not you can take it as a definition of a perfect gas.

The internal energy of a perfect gas depends only on its temperature.
 

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