# Difficulty understanding molar volume

Suppose I am at STP and I am dealing with an ideal gas and I have a 22.4L container (with a movable piston attached on top) filled with 1 mol gas. Now, I will try to change the molar volume in two ways:

Way 1

If I increase the pressure exerted on the ideal gas by decreasing the volume of the container, the molar volume will decrease.

Way 2

If I increase the pressure exerted on the ideal gas by injecting 1 mol more gas in the cylinder keeping the volume of the container constant (22.4L), the molar volume will change (I think). I think the molar volume will decrease.

Is my prediction right in way 2? If yes, then why am I not able to apply it here?

If my prediction in way 2 is wrong, could you please tell me why I am wrong?

• It must be a typo in your book Dec 6, 2021 at 19:00
• Right? I thought that too, so I saw another book, and the same thing was written. I'm so confused. Dec 6, 2021 at 19:02
• Well,,with all due respect to your books, they’re wrong. Dec 6, 2021 at 19:15
• Could you share the name of your book and pg number (preferably link though) Dec 14, 2021 at 16:07
• I don't do this for reputation points. I do this only to help people. I'm glad my answers were of help to you. Dec 17, 2021 at 11:27

Molar volume is defined by: $$V_m=M/\rho$$. M is molar mass , and $$\rho$$ is the density.
In both cases $$\rho$$ increases leading to a lower molar volume.