How does vapor pressure relate to intermolecular forces? | Socratic
, Deduce the relative volatility/rate of evaporation of substances when given The relative strength of intermolecular forces can often be determined by. Much less energy (in the form of heat) is required to break the intermolecular bonds of a volatile liquid than those of liquids having higher boiling points. These are attracted to one another by one or both of two forces: Van der Waal's ( induced dipole) forces; Dipole - dipole.
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.
There is no universally accepted definition of VOCs. Some regulatory entities define them in terms of their vapor pressure at ordinary temperatures, or their normal boiling points, or how many carbon atoms they contain per molecule, and others define them in terms of their photochemical reactivity.
Environmental Protection Agency currently defines them as any compound of carbonexcluding carbon monoxidecarbon dioxidecarbonic acidmetallic carbides or carbonatesand ammonium carbonatewhich participates in atmospheric photochemical reactions i. However, any such carbon compounds that have been determined to have a low photochemical reactivity, and specifically listed in the regulation, are exempted from regulation.
Wine making The wine industry uses the term volatile acids to refer to organic acids that are water-soluble, have short carbon chains six carbon atoms or less and which occur in wine. Cosmetics and flavorings Certain volatile oils obtained from plants have distinctive, pleasant aromas which are used in cosmetics and food flavorings. 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.
Volatility (chemistry) - encyclopedia article - Citizendium
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. 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.
11.5: Vaporization and Vapor Pressure
Thus diethyl ether ethyl etheracetone, and gasoline are volatile, but mercury, ethylene glycol, and motor oil are nonvolatile. 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 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.Which molecules have higher (or lower) vapor pressure
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: Which molecule corresponds to which curve?
Let us rank the species in order of increasing IM forces: