Q. What are the properties of liquids?
Ans.
Evaporation of Liquids
When we place a liquid in an open container, it slowly disappears. If we heat a liquid it disappears faster. This process is called evaporation.
Particles on the surface of a liquid experience less attraction than those inside the liquid. Therefore, particles on the surface escape the liquid if they have enough kinetic energy.
A higher temperature means that the molecules have a higher average kinetic energy. Therefore, more particles evaporate if the liquid is heated.
If the liquid is in a closed container, condensation of the vapor will eventually equal the process of evaporation. At that point, a dynamic equilibrium between these two opposing processes is reached.
Hydrogen Bonds
A type of bond seen in substances such as H2O is called a hydrogen bond. Liquids with hydrogen bonds tend to have high boiling points. Extra energy is required to break the hydrogen bonds. Hydrogen bonds are strong attractive forces that occur when a hydrogen of one molecule bonds to a neighboring electronegative atom of another molecule. Fluorine, oxygen, and nitrogen are the electronegative elements that typically form hydrogen bonds with a neighboring hydrogen molecule.
Vapor pressure of liquids
The gas pressure exerted by particles that have escaped from a liquid in a closed container is called the vapor pressure of the liquid. Vapor pressure varies with temperature.
The boiling point of a liquid is the temperature at which the vapor pressure of the liquid equals the atmospheric pressure. This condition results in boiling. At this temperature, particles go into the vapor state throughout the liquid in addition to those on the surface.
The normal, or standard, boiling point of a liquid is the temperature which produces a vapor pressure of 1 atm.
The freezing point is the temperature at which a liquid freezes to become a solid. This is also the temperature at which a solid melts, and therefore is also called the melting point of a solid.