Vapor pressure and intermolecular forces relationship help

How does vapor pressure relate to intermolecular forces? | Socratic

vapor pressure and intermolecular forces relationship help

The vapor pressure of a liquid is the equilibrium pressure of a vapor above its liquid (or solid); that is, the If the intermolecular forces between molecules are. The higher the vapor pressure will be if the IM forces are weak. the vapour pressure and consequently its boiling point will be higher. look at the relation b/ w the following: iOS · Android · Terms · Privacy · Site Map · Help. Acetone is a compound with no hydrogen bonding, and only polarity (along with London forces). At 25C, acetone has a vapor pressure of.

As the number of molecules in the vapor phase increases, the number of collisions between vapor-phase molecules and the surface will also increase.

Vapor Pressure - Chemistry LibreTexts

Eventually, a steady state will be reached in which exactly as many molecules per unit time leave the surface of the liquid vaporize as collide with it condense. At this point, the pressure over the liquid stops increasing and remains constant at a particular value that is characteristic of the liquid at a given temperature. The rate of evaporation depends only on the surface area of the liquid and is essentially constant. The rate of condensation depends on the number of molecules in the vapor phase and increases steadily until it equals the rate of evaporation.

Equilibrium Vapor Pressure Two opposing processes such as evaporation and condensation that occur at the same rate and thus produce no net change in a system, constitute a dynamic equilibrium. In the case of a liquid enclosed in a chamber, the molecules continuously evaporate and condense, but the amounts of liquid and vapor do not change with time. The pressure exerted by a vapor in dynamic equilibrium with a liquid is the equilibrium vapor pressure of the liquid.

vapor pressure and intermolecular forces relationship help

If a liquid is in an open container, however, most of the molecules that escape into the vapor phase will not collide with the surface of the liquid and return to the liquid phase.

Instead, they will diffuse through the gas phase away from the container, and an equilibrium will never be established.

Volatile liquids have relatively high vapor pressures and tend to evaporate readily; nonvolatile liquids have low vapor pressures and evaporate more slowly. Thus diethyl ether ethyl etheracetone, and gasoline are volatile, but mercury, ethylene glycol, and motor oil are nonvolatile.

vapor pressure and intermolecular forces relationship help

The equilibrium vapor pressure of a substance at a particular temperature is a characteristic of the material, like its molecular mass, melting point, and boiling point Table It does not depend on the amount of liquid as long as at least a tiny amount of liquid is present in equilibrium with the vapor. Molecules that can hydrogen bond, such as ethylene glycol, have a much lower equilibrium vapor pressure than those that cannot, such as octane.

The nonlinear increase in vapor pressure with increasing temperature is much steeper than the increase in pressure expected for an ideal gas over the corresponding temperature range.

vapor pressure and intermolecular forces relationship help

The temperature dependence is so strong because the vapor pressure depends on the fraction of molecules that have a kinetic energy greater than that needed to escape from the liquid, and this fraction increases exponentially with temperature. We say that the molecule has a permanent dipole. Now, the molecules line up.

The positive ends end up near to another molecule's negative end: Since this dipole is permanent, the attraction is stronger. However, we only see this sort of attraction between molecules that are polar. It is usually referred to as dipole - dipole interaction.

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.

vapor pressure and intermolecular forces relationship help

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.

Vapor Pressure and Boiling

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. Just having one of those species in the molecule is not enough.

11.5: Vapor Pressure

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.

vapor pressure and intermolecular forces relationship help

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.