Ideal Gases- Volume & pressure proportions

[fluoropHore]

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cant find this question specifically in forums, gonna shoot:
if the relationship to P & V for ideal gases is inverse and the graph plotted of P(x) vs V (Y) is asymptotic, then how come for questions asking about P vs V is linear?
Like if they ask how much does V decrease if you increase P by 2? Answer: 1/2

Yet, in TBR it specifically says it takes increasingly more P to compress a gas to volume V because the gas molecules are also increasing its P (see: gas-trapped P in manometer vs atmospheric P)... which way is it?

 

[fluoropHore]

Am I confusing the P of the gas inside the bulb mantometer to the gas of the atmosphere?

 

[fluoropHore]

So, are we to assume that only in IDEAL gases that it is inv proportional and that in real gases, since they take have intermol attractions/repulsions that at higher and higher Ps, the Vol changes less and less...?

 

[BB8730]

If everything else is constant, the P vs V relationship is inverse - not linear. Graphs of isothermal processes show this.

You can easily approach problems like this just using the Ideal gas law - PV = nRT. If you're only looking at P vs V, you can think of the equation like this - PV = X (where X = some constant). Then, to find how much V would change, rearrange the equation.

V = X/P

If P is doubled, V is halved.

Also, regarding your third post - an ideal gas is theoretical. As far as I know you should always use the Ideal gas law to approximate the behavior of gases and you shouldn't differentiate "ideal" gases and "real" gases.