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ideal gas Law says that

PV/T = nR

So does lets say you increase n and you Keep P and V constant should'nt the temperature decrease?

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  • $\begingroup$ Keeping the pressure constant while adding more particles requires removing heat from the particles already in the container, since the new particles will only add to the force on the walls, so this qualitatively makes sense. $\endgroup$ – probably_someone Sep 26 '18 at 10:40
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Yes indeed, temperature would decrease. This is because you are keeping the volume and pressure constant while the number of molecules increases. For a an intuitive explanation know that temperature is the average kinetic energy of the molecules.

Also notice that the higher the pressure means more force in collisions with the walls of the container per unit time, more molecules mean more force and more collisions per unit time provided that the velocity or the kinetic energy remains constant. Now notice that if the pressure remains same while the number of molecules increases, then the molecules must be be somehow moving slower(so there is now a lower force per molecule to balance the increase in total number of molecules) and hence if you can add molecules to a gas-system while keeping the pressure constant(suppose adding low energy or low temperature gas molecules) then the overall temperature of the system will decrease.

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Exactly. The more intuitive (at least for me) POV would be that you have to decrease the temperature to keep the pressure constant when you increase n.

It is comparable to the case of a pressure cooker where the pressure rises when you keep increasing the temperature but keep the volume and n constant.

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