[Laker12]

My book doesn't do a very good job explaining this, so any links or explanations would be appreciated:

By what factor does the avg velocity of a gaseous molecule increase whent he absolute temperate is doubled?

I'm trying to find a how average velocity corresponds to the absolute temperature but I can't find it anywhere.


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Which spicies is expected to have the highest boiling point at 1 am pressure?

O2, CO, CO2, or HCHO

[Mitch]

v_rms = (3RT/M)^1/2

[Yggdrasil]

v_rms = (3RT)^1/2

v_rms = (3RT/M)^1/2

In other words, the temperature of the gas is proportional to the kinetic energy of the gas molecules, and KE = (1/2)mv²

[Laker12]

I'm still a little unclear on how the average velocity is effected when the temp is doubled..

[Yggdrasil]

Temperature is proportional to kinetic energy

Kinetic energy is proportional to velocity squared

Therefore, temperature is proportional to velocity squared

If you double temperature, what happens to the velocity squared?  What happens to the velocity?

[Laker12]

Can you be a little clearer on how the temp is propertional to the velocity squared? I understand what you mean...sorta...but if you could get a little more technical using the question it'd really clarify it for me.

[Mitch]

If you double temperature, What happens to the velocity?

[Laker12]

You'd end up taking the square root of double the temperature?

[Yggdrasil]

Yup.  When temperature increases by a factor of 2, the rms velocity increases by a factor of sqrt(2).

[Laker12]

Lmao...it seems so simple now.

Anyone know about the second question?

[Yggdrasil]

Two approaches:

1) The compound with the highest boiling point will have the strongest intermolecular forces.

2)  Which one is liquid at RTP?

[Laker12]

If I wanted to use option 1, would I use the one with the biggest electronegativity?

[Yggdrasil]

Do you mean biggest difference in electronegativity?  Electronegativity is a property of atoms, not molecules.  However, differences in electronegativities leads to dipoles which are properties of molecules and do contribute to intermolecular forces.  However, a difference in electronegativity is not enough to give a molecule a net dipole moment and make it polar.  The geometry of the molecule has to be such that the dipoles from the various bonds do not cancel eachother out.

[Laker12]

Ok, how do I go about seeing which ones have the strongest intermolecular forces?

[Yggdrasil]

Here's a list of intermolecular forces from strongest to weakest:
1)  Ionic bond
2)  Hydrogen bond
3)  Dipole-dipole interaction
4)  Dipole-induced dipole interaction
5)  Van der Waals forces

For compounds with similar molecular weights, the compound with the strongest type of intermolecular force will have the highest boiling point.  So, what is the strongest type of intermolecular force present in each molecule?