GS-2 Physical Sciences Question 41

[behii208456]

the answer clearly proves that there is a decrease in volume, why is B not the correct choice then?

[mcat_premed3832]

The answer proves that there is a decrease in volume for the REAL gas (which of course, normally in nature, has at least some degree of intermolecular forces thus a real gas).

The explanation tries to underline the following:

Density D = m/v

Given that m is constant.

Given that the ideal gas has the lower density.

Conclusion: the ideal gas has the higher volume (opposite of answer choice B.).

Why would an ideal gas have a higher volume compared to a real gas? Ideally, it has no intermolecular forces so the molecules spread out.

[mytramta1691]

So is it any nonideal gas will have higher density than the ideal gas? Thanks

[jellywing_2058]

As mentioned in the explanation :

[mohsinalam5969]

@mytramta1691
Ideal Gas - Although no gas is truly ideal, many gasses follow the ideal gas law very closely at sufficiently low pressures. The ideal gas law was originally determined empirically and is simply

p V = n R T

p = absolute pressure (not gage pressure)
V = volume
n = amount of substance (usually in moles)
R = ideal gas constant
T = absolute temperature (not F or C)

Real Gas - Real gas laws try to predict the true behavior of a gas better than the ideal gas law by putting in terms to describe attractions and repulsions between molecules. These laws have been determined empirically or based on a conceptual model of molecular interactions or from statistical mechanics.
A well known real gas law is the van der Waals equation

( P + a / Vm2 )( Vm - b ) = R T

P = pressure
Vm = molar volume
R = ideal gas constant
T = temperature
where a and b are either determined empirically for each individual compound or estimated from the relations.
The answer proves that there is a decrease in volume for the REAL gas (which of course, normally in nature, has at least some degree of intermolecular forces thus a real gas).

The explanation tries to underline the following:
Density D = m/v
Given that m is constant

As it i clear that Ideal gases possess no intermolecular forces so its density should be less than that of any real gas.
So there is no non ideal gas which will have higher densisty than the ideal gas.