Expanding the Kinetic Theory THE NATURE OF LIQUIDS

OBJECTIVES When you complete this presentation, you will be able to discuss the assumptions of the kinetic theory with respect to liquids apply those assumptions to explain the behaviors of liquids with respect to evaporation vapor pressure boiling point

INTRODUCTION In some ways, liquids are like gases. They take the shape of their containers. They flow like dense gases. There are also differences between gases and liquids. Gas particles don’t feel the influence of other particles. Liquid particles feel attraction between the particles.

ASSUMPTIONS The distance between particles of a liquid are about the same magnitude as the size of the particles. This means that the individual liquid particles... feel attractive forces from the other particles in the liquid. do not move away from each other as do gases

ASSUMPTIONS The particles of a liquid are in constant, random motion. This means that the individual liquid particles... continue to move within the body of the liquid allow the liquid to conform to the shape of the container

APPLICATIONS Many of the properties of liquids (that are different from those of gases) show the balancing act between the increased attraction of the particles for each other and the movement of the particles

APPLICATIONS Liquids evaporate, that is, convert to gases at the surface of the liquid. This can be explained by looking at the action of the particles at the surface. Particles in the body of the liquid feel forces from all the surrounding particles.

APPLICATIONS Liquids evaporate, that is, convert to gases at the surface of the liquid. This can be explained by looking at the action of the particles at the surface. Particles on the surface of the liquid only feel about half the forces that particles in the body of the liquid feel from the surrounding particles.

APPLICATIONS Liquids evaporate, that is, convert to gases at the surface of the liquid. This can be explained by looking at the action of the particles at the surface. The movement of particles on the surface of the liquid allows some of them to move away from the surface as a gas particle.

APPLICATIONS Liquids have a vapor pressure, which is a measure of the force exerted by the gas over the surface of the liquid. This is related to evaporation. Just as liquids evaporate to form gases, gases condense to form liquids. This is an equilibrium system. Liquid Gas

APPLICATIONS Liquids have a vapor pressure, which is a measure of the force exerted by the gas over the surface of the liquid. The vapor pressure of a liquid is related to the temperature of the system. The vapor pressure increases as the temperature increases.

APPLICATIONS Liquids also have a boiling point which is the temperature at which the liquid is converted to a gas. The boiling point is the temperature where the vapor pressure equals the atmospheric pressure. For water, the vapor pressure at 100°C (273 K) is atm. At lower pressures, the boiling point is lower. At the top of Mt. Everest pressure is atm water boils at 70°C.

APPLICATIONS Liquids are much denser than gases. The attraction of the particles of a liquid for the other particles of the liquid keeps the particles closer together than the particles of a gas. This increases the number of particles in a given volume. This results in an increase in density.

SUMMARY We extend the assumptions of the Kinetic Theory to explain the behavior of liquids. The distance between particles of a liquid are about the same magnitude as the size of the particles. The particles of a liquid are in constant, random motion. The properties of liquids are a balancing act between these assumptions.