Figure 13.5 Both liquids and gases can flow. The liquid on the left is colored water. The gas on the right is bromine vapor. If a gas is denser than air, it can be poured from one container into another. These pictures were taken in a fume hood because bromine is both toxic and corrosive.
2. Figure 13.6a eventually moves into the air. The conversion of a liquid to a gas or vapor is called vaporization. When such a conversion occurs at the surface of a liquid that is not boiling, the process is called evaporation. Most of the molecules in a liquid don’t have enough kinetic energy to overcome the attractive forces and escape into the gaseous state. During evaporation, only those molecules with a certain minimum kinetic energy can escape from the surface of the liquid. Even some of the particles that do escacape collide with molecules in the air and rebound into the liquid. Figure 13.6 The process of evaporation has a different outcome in an open system, such as a lake, than in a closed system, such as a terrarium. (a) In an open container, molecules that evaporate can escape from the container. (b) In a closed container, the molecules cannot escape. They collect as a vapor above the liquid. Some molecules condense back into a liquid.
3. Most solid substances are crystalline. In a crystal the particles are arranged in an orderly, repeating, three-dimensional pattern called a crystal lattice. Figure 13.10 shows part of the crystal lattice in sodium chloride. The shape of a crystal reflects the arrangement of the particles within the solid.
Figure 13.10 The orderly arrangement of sodium and chloride ions within a sodium chloride crystal determines the shape of the crystal. The closely packed ions vibrate around fixed points on the crystal.
1. 1. For Experiment 1, place one drop of water in the Petri dish. Replace the cover and place a small piece of ice on top of the cover.
2. After a few minutes, observe the interior surface of the Petri dish cover and the contents of the dish. Record your observations. Clean and dry the Petri dish and cover. 3. Repeat Steps 2 and 3 for Experiments 2–5, using the materials listed in the table. For Experiment 4, place the Petri dish on the graph paper so that you can place the water and the calcium chloride about 3 cm apart. 5. If you hang wet laundry on a clothesline on a very cold day, the water in the clothes quickly freezes to ice. Eventually, however, the clothes become dry although the ice never thaws. The ice changes directly to water vapor without melting and passing through the liquid state. The change of a substance from a solid to a vapor without passing through the liquid state is called sublimation. Sublimation can occur because solids, like liquids, have a vapor pressure. Sublimation occurs in solids with vapor pressures that exceed atmospheric pressure at or near room temperature. Iodine is another example of a substance that undergoes sublimation. This violet-black solid ordinarily changes into a purple vapor without passing through a liquid state. Notice in Figure 13.14 how dark crystals of iodine deposit on the underside of a watch glass placed on top of a beaker containing solid iodine that is being heated. The iodine vapor sublimes from iodine crystals in the bottom of the beaker and condenses to form crystals on the watch glass.
Figure 13.14 When solid iodine is heated, the crystals sublime, going directly from the solid to the gaseous state. When the vapor cools, it goes directly from the gaseous to the solid state. Sublimation has many useful applications. If freshly brewed...