Kinetic energy of gases with same volume, pressure, mass, but different MW (EK chem Q101)

[rlaboss]

Consider two gases A and B with different molecular weights in fixed containers of the same volume and pressure: A=0.35g B=0.35g.

All of the following are true accept:

A) both gases have the same average kinetic energy
B) the volumes of a molecule of gas A and a molecule of gas B are equal
C) the average force exerted on the container by gas A is the same as that exerted by gas B
D) The molecules of gas A exert no forces on each other when no colliding

Apparently the answer is A, which would be true if it was per molecule or per mole, but I think both gases collectively have the same kinetic energy total.

in PV=nRT, and P and V are the same between A and B, then nT must be the same for both A and B. if KE per mole = (3/2)RT, then KE per n moles = (3/2)nRT. If nT is equal for both A and B, then shouldn't they have the same kinetic energy?

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[rlaboss]

In other words, when kinetic molecular theory states that the average KE is directly proportional to temperature of the gas, is that per molecule or for the gas as a whole. If you had the same gas under the same pressure and temperature, but the number of molecules and volume were doubled, would the kinetic energy of the gas as a whole be doubled? Does the entire system even have a KE or is it just something to describe the individual molecules themselves?

 

[Nugester]

For an ideal gas, individual molecules would have different velocities at a given temperature. However, average KE refers to the gas as a whole and since KE = 3/2kT, for the question above, both ideal gases should have the same average KE.

 

[rlaboss]

For an ideal gas, individual molecules would have different velocities at a given temperature. However, average KE refers to the gas as a whole and since KE = 3/2kT, for the question above, both ideal gases should have the same average KE.

I understand that average KE of each molecule in the gas is 3/2kT. Another way to frame it would be: If the average KE per molecule was the same for two containers of gas, but one container had twice the molecules, could we say that gas (as a whole) has twice the KE?