CK-12-Chemistry Intermediate

13.2. Liquids http://www.ck12.org

MEDIA

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Lesson Summary

• Intermolecular forces keep the particles of liquids close together, but, due to relatively loose associations
  between any two particles, liquids are still able to flow freely.


• Surface tension is a property of liquids that makes it slightly more favorable for a liquid to minimize its surface
  area. This can lead to interesting properties, such as the ability of certain objects to float on the surface of a
  liquid even if they are denser than that liquid.


• Molecules of a liquid evaporate even when the temperature of the liquid is below its boiling point. Molecules
  with high kinetic energies escape the surface of the liquid, leaving the remaining liquid cooler than it was
  before.


• The vapor pressure of a liquid is determined by the strength of the intermolecular forces between its particles.
  Vapor pressure increases as temperature increases due to an increased rate of evaporation. The relationship
  between vapor pressure and temperature is shown on a vapor pressure curve.


• The boiling of a liquid occurs when its vapor pressure is equal to the external pressure.

Lesson Review Questions

Reviewing Concepts

1. Explain why gases are compressible, while liquids are almost completely incompressible.


2. Explain how a molecule of a liquid evaporates in terms of its kinetic energy. Why does the rate of evaporation
   increase with temperature?


3. When a highly volatile (evaporates rapidly) liquid such as acetone is spilled on your skin, it feels cold even if
   the liquid is originally at room temperature. Explain why this is true.


4. A liquid in a closed container has a constant vapor pressure. What can be said about the rate of evaporation of
   the liquid compared to the rate of condensation of the vapor?


5. Explain how the boiling point of a liquid varies with the atmospheric pressure.


6. What is the difference between boiling point and normal boiling point?


7. Liquid A has weaker intermolecular forces than liquid B.

a. Which liquid has the higher vapor pressure?

b. Which liquid has a higher normal boiling point?

c. Which liquid would demonstrate greater surface tension?

Problems

8. Use the vapor pressure curve of water to answer the following questions.