L1.2: The Liquid State

• • Evaporation is the conversion of liquids into the gas phase.

  • Evaporation is endothermic, it absorbs heat from the surroundings.
• • Condensation is the conversion of gases into the liquid phase.

  • Condensation is exothermic, it gives off heat to the surroundings.
• • Vapor pressure is the pressure exerted by gas molecules in equilibrium with the liquid phase.

  • Vapor pressure increases with increasing temperature.

  • The boiling point of a liquid is the temperature at which its vapor pressure = 760 mmHg.
• •The stronger the intermolecular forces, the lower the vapor pressure at a given temperature.
• Viscosity is a measure of a fluid’ s resistance to flow freely.

  •A viscous liquid feels “thick.”

  •Compounds with strong intermolecular forces tend to be more viscous than compounds with weaker forces.

  •Substances composed of large molecules tend to be more viscous, too, because large molecules do not slide past each other as freely.
• Surface tension is a measure of the resistance of a liquid to spread out.

  •Interior molecules in a liquid are surrounded by intermolecular forces on all sides.

  •Surface molecules only experience intermolecular forces from the sides and from below.
• •The stronger the intermolecular forces, the stronger the surface molecules are pulled down toward the interior of a liquid and the higher the surface tension.

  •Water has a very high surface tension because of its strong intermolecular hydrogen bonding.

  •When small objects seem to “float” on the surface of water, they are held up by the surface tension only.