# Molecules' mean square speed

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The answer to this question is B which makes sense because the mean square speed for the molecules is calculated using the individual speeds of them all.

But the question specifies "at the same temperature", therefore, how would the mean square speed differ if id the molecules would have different temperatures?

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(Original post by

The answer to this question is B which makes sense because the mean square speed for the molecules is calculated using the individual speeds of them all.

But the question specifies "at the same temperature", therefore, how would the mean square speed differ if id the molecules would have different temperatures?

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**jtbteddy**)The answer to this question is B which makes sense because the mean square speed for the molecules is calculated using the individual speeds of them all.

But the question specifies "at the same temperature", therefore, how would the mean square speed differ if id the molecules would have different temperatures?

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Could you give a reference for the source of this question and the source of the answer.

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Where does it say the answer is B?

Could you give a reference for the source of this question and the source of the answer.

**Stonebridge**)Where does it say the answer is B?

Could you give a reference for the source of this question and the source of the answer.

Q1

http://www.edexcel.com/migrationdocu...s_20110817.pdf

Oops. My bad, the answer is A. Im guessing this is found using 1/2m^2 = 3/2kT ?

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At the same temperature the mean kinetic energy of the molecules is the same.

If the molecules are lighter they need a higher mean (square) speed to have the same energy as a heavier molecule.

If the molecules are lighter they need a higher mean (square) speed to have the same energy as a heavier molecule.

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At the same temperature the mean kinetic energy of the molecules is the same.

If the molecules are lighter they need a higher mean (square) speed to have the same energy as a heavier molecule.

**Stonebridge**)At the same temperature the mean kinetic energy of the molecules is the same.

If the molecules are lighter they need a higher mean (square) speed to have the same energy as a heavier molecule.

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**Stonebridge**)

At the same temperature the mean kinetic energy of the molecules is the same.

If the molecules are lighter they need a higher mean (square) speed to have the same energy as a heavier molecule.

http://www.edexcel.com/migrationdocu...e_20120618.pdf

http://www.edexcel.com/migrationdocu...s_20120816.pdf

The mixture has a mixture of gases, each with a different mass. Higher mass molecules have a lower speed, and viceversa for lower mass molecules, don't they? So why is the answer D?

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(Original post by

On this paper, I had marked B for Q1 based on what we spoke about here, but the answer is D, why so?

http://www.edexcel.com/migrationdocu...e_20120618.pdf

http://www.edexcel.com/migrationdocu...s_20120816.pdf

The mixture has a mixture of gases, each with a different mass. Higher mass molecules have a lower speed, and viceversa for lower mass molecules, don't they? So why is the answer D?

**jtbteddy**)On this paper, I had marked B for Q1 based on what we spoke about here, but the answer is D, why so?

http://www.edexcel.com/migrationdocu...e_20120618.pdf

http://www.edexcel.com/migrationdocu...s_20120816.pdf

The mixture has a mixture of gases, each with a different mass. Higher mass molecules have a lower speed, and viceversa for lower mass molecules, don't they? So why is the answer D?

It is asking about the

**kinetic energy**of the molecules,

**not**their mean square speed.

At the same temperature, the mean kinetic energies are the same.

The lighter molecules do move faster but that is not what the question is asking for.

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(Original post by

You are not reading the question.

It is asking about the

At the same temperature, the mean kinetic energies are the same.

The lighter molecules do move faster but that is not what the question is asking for.

**Stonebridge**)You are not reading the question.

It is asking about the

**kinetic energy**of the molecules,**not**their mean square speed.At the same temperature, the mean kinetic energies are the same.

The lighter molecules do move faster but that is not what the question is asking for.

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