EK 1001 chemistry Q 199 & 200: Kinetic Molecular theory

[Sarahka74]

Question 199:
The average molecular KE of a sample of CO2 is found to be the same as a sample of neon. How do the temperatures compare?

A: The temperatures of the two samples are the same.

I understand this, because KE is just way of representing temperature,

Question 200:
The average speed of the molecules in a sample of carbon dioxide is found to be the same as a sample of neon. How do the temperatures of the sample compare?

A:The temperature of carbon dioxide is roughly two times the temperature of neon


If question 199 is true, then how can question 200 be as well? Can someone explain the theory behind why the answers for 199 & 200 are what they are?

Thank you for your help.

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[laczlacylaci]

For 199:
KE=3/2RT
If you were told that the KE is the same, then T must be the same because R is a constant.

For 200:
KE=1/2mv^2=3/2RT
You know that CO2 Molar Mass (36)>Ne Molar Mass (20), and if you were given that v is the same for both, then CO2 T>Ne T.

 

[betterfuture]

If 2 samples of gas have the same average KE, then their Temperatures are the same since regardless of what gases they are. However, when asked about individual speed, they could be different depending on their masses.

Example: If the force on Ball A is equal to the force on Ball B, but Ball A is twice the mass of Ball B, the acceleration of Ball A has to be 1/2 that of Ball B. This way, their forces stay the same.