PROPERTIES OF LIQUID

• Have you ever observed small insects walking on the surface of the water?

  
• In nature, there are attractive and repulsive forces. Some of these attractive forces also exist among very small particles of matter.
• In the previous lesson, you have described the different types of intermolecular forces of attraction present between molecules and learned how to predict the intermolecular forces between specific molecules.
• In this lesson, you will discuss the different properties of liquids that arise from IMFAs and the importance of each property that affect the things around us.
• Properties of liquids


  Surface tension, viscosity, vapor pressure, boiling point, heat of vaporization
• States of matter


  • Solids have strong intermolecular forces, liquids have intermediate intermolecular forces, gases have weak intermolecular forces

  
• The properties of liquids can be attributed to the intermolecular forces of attraction that hold the molecules together in order to occupy a volume of a certain space of a container.
• These intermolecular forces of attraction are directly related to the surface tension, viscosity and vapor pressure of the liquid.
• Surface tension


  The tendency of a fluid to acquire the least possible surface area

  
• A drop of liquid is assumed to be spherical in shape due to the intermolecular forces of attraction present in the molecules of the liquids.

  
• Water striders can walk on water because of surface tension.
• Cohesion


  The attraction between like molecules
• Adhesion


  The attraction between unlike molecules
• Droplets of water on the waxy surface of an apple.
• Capillary action


  When adhesive forces are greater than cohesive forces, a concave meniscus forms. When adhesive forces are less than cohesive forces, a convex meniscus forms.
• Viscosity


  The measure of a fluid's resistance to flow
• Liquids that flow easily have low viscosity while liquids that do not flow readily have high viscosity.
• Molecules with stronger intermolecular forces have greater resistance to flow because it is difficult for the molecules to move and slide past one another.
• When the temperature is high, the molecules have more energy and it becomes easier to overcome the IMFA. This leads to lower viscosity.
• For liquids, viscosity decreases with increasing temperature, but for gases, the viscosity increases with increasing temperature.
• Enthalpy of vaporization


  The heat required to induce the phase change from liquid to gas
• Vaporization occurs more readily with increased temperature, increased surface area of the liquid, and decreased strength of intermolecular forces.
• The enthalpy of vaporization is the quantity of heat that must be absorbed if a certain quantity of liquid is vaporized at a constant temperature.
• Vapor pressure


  The pressure exerted by a vapor in equilibrium with its liquid phase in a closed system
• Molecules with stronger intermolecular forces have less tendency to escape into gas, and thus, have lower vapor pressure compared to those with weaker IMFA.
• Solubility


  The ability of a substance to dissolve in a given amount of solvent at a specified temperature
• Like dissolves like. When the solute and the solvent both exhibit the same intermolecular forces of attraction, they form a solution.
• If two liquids dissolve or mix together, they are called miscible liquids. If two liquids do not dissolve or mix together, they are called immiscible liquids.
• Hydrophilic


  Substances or molecules that form interactions with water
• Hydrophobic


  Substances or molecules that repel water
• Amphipathic molecules


  Molecules with both hydrophilic and hydrophobic regions
• Soap and detergent molecules have hydrophilic heads and hydrophobic tails.
• The stronger the intermolecular forces between the solvent molecule and the solute molecule, the greater the solubility.
• Boiling point


  The temperature at which a substance changes from liquid to gas
• Boiling happens when the molecules of a liquid gain enough energy to overcome the intermolecular forces of attraction that hold the molecules together.
• Stronger intermolecular forces mean a greater amount of energy is needed to break the attractive forces between molecules.
• Hydrogen bonding makes the boiling point of water significantly higher than similar binary compounds of hydrogen and a Group 6A element.
• Boiling point increases as mass and surface area increases.
• Surface tension is the tendency of a fluid to acquire the least possible surface area. Liquids with strong IMFA have high surface tension.

  
• Viscosity is the measure of a fluid's resistance to flow. Molecules with stronger IMFA have higher viscosity compared to those with weaker IMFA. Higher temperature leads to lower viscosity.