Average Kinetic Energy Question - help please

[tgutberg]

Here is a question:

Two identical tanks are filled with gas at 20C. Both gases are at 1 atm. If one tank contains helium and the other neon then:
a. the atoms in both tanks are moving at the same average speed.
b. the average kinetic energy of the neon atoms is greater than that of the helium.
c. the average kinetic energy of the neon atoms is less than that of helium
d. both tanks contain the same number of gas atoms.
e. the density of the gas in both tanks is the same

The correct answer is D.
In the answer explanation they say that according to the theory all ideal gasses at the same temperature and pressure will have the same average kinetic energy. That is fine but isnt that exactly answer A? I thought the average kintetic energy is exactly the same at average speed.

Where am I wrong? Help would be appreciated

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[sacjumpman]

Here is a question:

Two identical tanks are filled with gas at 20C. Both gases are at 1 atm. If one tank contains helium and the other neon then:
a. the atoms in both tanks are moving at the same average speed.
b. the average kinetic energy of the neon atoms is greater than that of the helium.
c. the average kinetic energy of the neon atoms is less than that of helium
d. both tanks contain the same number of gas atoms.
e. the density of the gas in both tanks is the same

The correct answer is D.
In the answer explanation they say that according to the theory all ideal gasses at the same temperature and pressure will have the same average kinetic energy. That is fine but isnt that exactly answer A? I thought the average kintetic energy is exactly the same at average speed.

Where am I wrong? Help would be appreciated

Kinetic Energy = 1/2(mass)(velocity)^2

Also KE = 3/2(k)(T)
where k is Boltzmann constant and T is temp in Kelvin.

Thus KE is only dependent on the temperature and KE will be equal at equal temperature.

However, because one molecule/atom is heavier than the other, it will have a smaller velocity (due to first equation).

 

[ucla2134]

Here is a question:

Two identical tanks are filled with gas at 20C. Both gases are at 1 atm. If one tank contains helium and the other neon then:
a. the atoms in both tanks are moving at the same average speed.
b. the average kinetic energy of the neon atoms is greater than that of the helium.
c. the average kinetic energy of the neon atoms is less than that of helium
d. both tanks contain the same number of gas atoms.
e. the density of the gas in both tanks is the same

The correct answer is D.
In the answer explanation they say that according to the theory all ideal gasses at the same temperature and pressure will have the same average kinetic energy. That is fine but isnt that exactly answer A? I thought the average kintetic energy is exactly the same at average speed.

Where am I wrong? Help would be appreciated

I think you got it wrong because you confused between average speed and average kinetic energies which are not the same. Average kinetic energy only depend on Temperature, whereas speed is depend on mass:
Ek=(1/2)KT
speed is inversely proportional to mass. Hope it helps

 

[sacjumpman]

I think you got it wrong because you confused between average speed and average kinetic energies which are not the same. Average kinetic energy only depend on Temperature, whereas speed is depend on mass:
Ek=(1/2)KT
speed is inversely proportional to mass. Hope it helps

Double check that: KE = (3/2)kT = 1/2mv^2