Consider two gases, A and B, each in a 1.0L container with both gases at the same temperature and pressure...?

Question

The mass of gas A in containerA is 0.34g and the mass of gas B in containerB is 0.48g
a.which gas sample has the most molecules present?explain
b. which gas sample has the largest average kinetic energy. explain.
c. which gas sample has the fastest average kinetic velocity? explain
d. how can the pressure in the 2 containers be equal to each other since the larger gas B molecules collide with the container walls more forcefully?

My answers: can someone please check me? if anyone can give me a better explanation than my vague ones, it would be appreciated!!
a) both gas samples have the same molecules because the two gases are at STP
b) They are equal in the average kinetic energy because the average kinetic energy is proportional to the temperature and they both are under the same temperature.
c) Gas A has the fastest average velocity because it has a smaller mass (any equation i can use to prove this?)
d) gas A collides with the wall more frequently

Answer 1

All your answers are OK. But the problem is NOT OK.
a) The problem did not specify whether both gases are ideal or not. If they are ideal gases, both gas samples have exactly the same numbers of molecules because both gases are at the same temperature and pressure. Do NOT claim STP, since you do not know the temperature. But if the gases are not ideal gases, they can easily have a difference of a few molecules.
b) The problem did not specify whether both gases are mono-atomic, diatomic, or polyatomic gases. Except mono-atomic gases, all other gases have rotational kinetic energy thus their average kinetic energy would be higher than the average kinetic energy of any mono-atomic gases. Since the problem does not specify, we may only guess that the problem implies "average TRANSLATIONAL kinetic energy"
c) Again, the problem failed to specify "average TRANSLATIONAL kinetic energy" thus cause confusions.
To prove your conclusion, let n be the number of moles for both A and B. Thus 0.34g/n is the molar mass for A and 0.48g/n is the molar mass for B. Obviously 0.34g/n < 0.48g/n, thus A has a smaller molar mass. According to molecular kinetic theory, the average speed of the molecule is: sqrt(8*k*T/(pi*m)) (see reference), which is inversely proportional to the square-root of molecular mass m. Hence molecules of gas A has faster average velocity (than B).
d) You are perfectly fine.