We know the ideal gas equation is PV=nRT,then, according to this,if we keep Pressure,volume to be constant,then on increasing temperature,no of moles will reduce,this would mean that mass of matter or particles of the gas would simply vanish????how????how is conservation of mass followed here?

  • 4
    $\begingroup$ How are you going to keep the pressure constant? And please refrain from improper terms like "temp", "no", "number of moles" etc. as well as illiterate punctuation. $\endgroup$
    – andselisk
    May 4, 2023 at 14:10
  • $\begingroup$ Do not try to put as much info to the title as possible. Think about titles like magazine or newspaper headlines. $\endgroup$
    – Poutnik
    May 4, 2023 at 14:13

1 Answer 1


There are only 2 ways how to change the molar amount of gas ($n$) in the system:

  • We add/remove some gas, so the system is open and the mass conservation law does not apply on the system content.
  • There is ongoing chemical ( or nuclear ) reaction with different number of reactant and product entities and $n$ is changing due that.

Otherwise, $n$ is given as a fixed parameter. As $R \approx \pu{8.314 J K-1 mol-1}$ is a physical constant, we can reduce equation

$$pV = nRT$$


$$\frac{pV}{T} = a$$

where $a = nR$.

We can freely change any two of all three quantities ($p$, $V$, $T$), but the remaining third one is fully determined by values of the other two.

So $p=f(T,V)$, or $V=f(T,p)$ or $T=f(p,V)$.


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