Different volatilities in ideal solutions?

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In summary, when comparing two liquids, if the intermolecular forces between molecules of one liquid are greater than the other, then the first liquid is more volatile. When mixing these liquids to create a solution, the solution is considered ideal if the tendency for molecules to leave the solution to the gas phase remains unchanged. This can be achieved if the new interactions between the two types of molecules are equal to their respective individual intermolecular forces. However, this is not the only way for an ideal solution to form, as long as the sum of the intermolecular forces between the two types of molecules is equal to twice the new interaction force. So, the volatilities of the two liquids may not necessarily be the same in this case.
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SilverSoldier
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Suppose ##A## and ##B## are two liquids, and intermolecular forces between molecules of ##A## are of magnitude ##f_{AA}## and between molecules of ##B##, ##f_{BB}##. If ##f_{AA}>f_{BB}##, then the pure liquid ##A## is volatile than ##BB##, i.e., the tendencies that the molecules have to leave liquid phase to the gas phase depends on the intermolecular forces between them.

Say we mix ##A## and ##B## to make a solution. From my understanding, such a solution is said to be ideal, if the tendencies that the molecules of ##A## and ##B## have to leave the solution to the gas phase remain unchanged upon mixing.

Now certainly, once the liquids are mixed, molecules of ##A## will interact with those of ##B##, and new intermolecular interactions will form between them; let us say of magnitude ##f_{AB}##.

If the tendency of molecules of ##A## to leave the liquid must remain unchanged, the new interactions it forms with molecules of ##B## must be of the same magnitude as ##f_{AA}##, so ##f_{AA}=f_{AB}##, or the tendency should change. Similarly, for the tendency of molecules of ##B## to leave the solution to not change, ##f_{BB}=f_{AB}##.

But then ##f_{AA}=f_{BB}##, so the liquids must have the same volatilities. Is this so? Have I misunderstood anything?
 
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SilverSoldier said:
If the tendency of molecules of ##A## to leave the liquid must remain unchanged, the new interactions it forms with molecules of ##B## must be of the same magnitude as ##f_{AA}##, so ##f_{AA}=f_{AB}##, or the tendency should change. Similarly, for the tendency of molecules of ##B## to leave the solution to not change, ##f_{BB}=f_{AB}##.

But then ##f_{AA}=f_{BB}##, so the liquids must have the same volatilities. Is this so? Have I misunderstood anything?
Yes, you misunderstood something
The situation ##f_{AA}=f_{BB}=f_{AB}## is one option to have ideal solution, but not the only one.
Consider four molecules - two A and two B molecules.
When the pairs change, they form two pairs of AB.
Therefore, it is sufficient that
##f_{AA}+f_{BB}=2*f_{AB}##
 

FAQ: Different volatilities in ideal solutions?

1. What is volatility in ideal solutions?

Volatility in ideal solutions refers to the tendency of a substance to evaporate or vaporize at a given temperature. It is a measure of how easily a substance can transition from a liquid to a gas phase.

2. How do different volatilities affect the behavior of ideal solutions?

Different volatilities in ideal solutions can affect the overall vapor pressure, boiling point, and composition of the solution. Substances with higher volatilities will have a greater effect on the vapor pressure and boiling point of the solution.

3. What factors can influence the volatility of a substance in an ideal solution?

The volatility of a substance in an ideal solution can be influenced by factors such as intermolecular forces, molecular weight, and temperature. Substances with weaker intermolecular forces and lower molecular weight tend to have higher volatilities.

4. How does Raoult's Law relate to different volatilities in ideal solutions?

Raoult's Law states that the vapor pressure of an ideal solution is proportional to the mole fraction of each component in the solution. Therefore, substances with higher volatilities will have a greater impact on the overall vapor pressure of the solution.

5. Can different volatilities in ideal solutions lead to deviations from Raoult's Law?

Yes, deviations from Raoult's Law can occur when there are significant differences in the volatilities of the components in an ideal solution. This can result in a non-ideal solution, where the vapor pressure is not directly proportional to the mole fraction of each component.

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