Volatility (chemistry) - encyclopedia article - Citizendium
The effect of entropy is to make everything a gas, since that is the most random arrangement of molecules. The effect of energy in these cases is to cause. The vapor pressure of a substance is the pressure at which its gas. The only thing that prevents these molecules from escaping (assuming approximately the same molecular weight) is the intermolecular forces.
In other words, the higher is the vapor pressure of a liquid, the higher is the volatility and the lower is the normal boiling point of the liquid. The adjacent vapor pressure chart graphs the dependency of vapor pressure upon temperature for a variety of liquids  and also confirms that liquids with higher vapor pressures have lower normal boiling points.
For example, at any given temperature, methyl chloride CH3Cl has the highest vapor pressure of any of the liquids graphed in the chart. In terms of intermolecular forcesthe boiling point represents the temperature at which the liquid molecules possess enough kinetic energy to overcome the various intermolecular attractions binding the molecules to each other within the liquid.
Therefore the boiling point is also an indicator of the strength of those attractive forces. The higher the intermolecular attractive forces are, the more difficult it is for molecules to escape from the liquid and hence the lower is the vapor pressure of the liquid.
How does vapor pressure relate to intermolecular forces? | Socratic
The lower the vapor pressure of the liquid, the higher the temperature must be to initiate boiling. Thus, the higher the intermolecular attractive forces are, the higher is the normal boiling point.
Relative volatility refers to a measure of the difference between the vapor pressure of the more volatile components of a liquid mixture and the vapor pressure of the less volatile components of the mixture. This measure is widely used in designing large industrial distillation processes.
The use of relative volatility applies to multi-component liquid mixtures as well as to binary mixtures. Volatile Organic Compound For more information, see: The term Volatile organic compound VOC refers to organic chemical compounds having significant vapor pressures and which can have adverse effects on the environment and human health.
VOCs are numerous, varied and include man-made anthropogenic as well as naturally occurring chemical compounds. The anthropogenic VOCs are regulated by various governmental environmental entities worldwide. The strength of this attraction increases with increasing total number of electrons. Hydrogen bond Hydrogen is a special element. Because it is really just a proton, it turns out that it can form a special type intermolecular interaction called the hydrogen bond.
If the hydrogen in a moleucle is bonded to a highly electronegative atom in the second row only N, O, or Fa hydrogen bond will be formed. In essence the three elements listed above will grab the electrons for itself, and leave the hydrogen atom with virtually no electron density since it had only the one. Now, if another molecule comes along with a lone pair, the hydrogen will try to position itself near that lone pair in order to get some electron density back.
This ends up forming a partial bond, which we describe as the hydrogen bond. The strength of this interaction, while not quite as strong as a covalent bond, is the strongest of all the intermolecular forces except for the ionic bond.
A diagram of the hydrogen bond is here: Could the CH2O molecule exhibit hydrogen bonding? The answer is no, since the hydrogen must be bound to either N, O, or F.
Organic chemistry: - Volatility
Just having one of those species in the molecule is not enough. Trends in the forces While the intramolecular forces keep the atoms in a moleucle together and are the basis for the chemical properties, the intermolecular forces are those that keep the molecules themselves together and are virtually responsible for all the physical properties of a material. The intermolecular forces increase in strength according to the following: Therefore, one would expect the melting and boiling points to be higher for those substances which have strong intermolecular forces.
We know that it takes energy to go from a solid to a liquid to a gas.
This energy is directly related to the strength of attraction between molecules in the condensed phases. Since energy is directly proportional to the temperature, the above trends ought to hold true. In addition, there are energies associated with making these phase transitions: Each of these processes are endothermic, and scale with the magnitude of the intermolecular forces.
Thus, as these intermolecular forces increase, so do the energies requires to melt, vaporize, or sublime go from solid to a gas a species. Every substance also has an associated vapor pressure with it. The vapor pressure is defined to be the amount of gas of a compound that is in equilibrium with the liquid or solid. If the intermolecular forces are weak, then molecules can break out of the solid or liquid more easily into the gas phase.
Consider two different liquids, one polar one not, contained in two separate boxes. We would expect the molecules to more easily break away from the bulk for the non-polar case.
This would mean that, proportionately, there are more molecules in the gas phase for the non-polar liquid. This would increase the vapor pressure. Thus, unlike the physical properties listed above, the vapor pressure of a substance decreases with increasing intermolecular forces.
Now, as an example, we will plot vapor pressure as a function of temperature for three compounds: