![]() The equation would look like P solvent = X solvent P o solvent. If we simply multiply the new mole fraction of solvent by the standard vapor pressure (P o solvent) of the pure solvent, this will give us a good approximation of the new vapor pressure of the solvent. In order to figure out how much the solute has affected the vapor pressure, we need to approximate how many fewer molecules are able to reach the surface of the liquid, correct? A good approximation of how many molecules there are of solvent versus solute is the mole fraction, X solvent. Since only solvent molecules located at the surface can escape (evaporate), the sheer presence of the solute lowers the number of solvent molecules coming and going and therefore lowers the equilibrium vapor pressure. What happens to the system if we add a solute to the solvent in question? Well, in the simplest terms, since some of the solute molecules will take up spaces at the surface of the liquid, this will limit the number of solvent molecules at the surface. a bottle of coke), and also the intermolecular forces of the liquid itself (stronger bonds will require more kinetic energy to break slowing the evaporation process, lowering the overall vapor pressure of the system). This vapor pressure is dependent on a number of factors, including the temperature of the system (kinetic energy is required to help the molecules escape into the gas phase), the pressure of the system (high pressure can keep the gas contained in the liquid e.g. The pressure of the vapor phase above the liquid at this point is called the equilibrium vapor pressure. In a closed container, a liquid will evaporate until an equal amount of molecules are returning to the liquid state as there are escaping into the gas phase. Let's first remind ourselves about what vapor pressure is and what affects it chemically and physically. Colligative properties include vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure. ![]() ![]() Colligative properties of solutions are properties that depend upon the concentration of solute molecules or ions, but not upon the identity of the solute.
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