Liquids and Solids Chapter 12

The Structure of Solids, Liquids, and Gases

Liquids The particles in a liquid are closely packed, but they have some ability to move around. The close packing results in liquids being incompressible. But the ability of the particles to move allows liquids to take the shape of their container and to flow. However, they don’t have enough freedom to escape and expand to fill the container(s).

Strong intermolecular forces Properties of Liquids Surface tension is the amount of energy required to stretch or increase the surface of a liquid by a unit area. Strong intermolecular forces High surface tension 12.3

Properties of Liquids Cohesion is the intermolecular attraction between like molecules Adhesion is an attraction between unlike molecules Adhesion Cohesion 12.3

Ice is less dense than water Water is a Unique Substance Maximum Density 40C Density of Water Ice is less dense than water 12.3

Solids The particles in a solid are packed close together and are fixed in position. Though they are vibrating. The close packing of the particles results in solids being incompressible. The inability of the particles to move around results in solids retaining their shape and volume when placed in a new container, and prevents the particles from flowing.

Solids, Continued Some solids have their particles arranged in an orderly geometric pattern. We call these crystalline solids. Salt and diamonds. Other solids have particles that do not show a regular geometric pattern over a long range. We call these amorphous solids. Plastic and glass.

Escaping from the Surface The process of molecules of a liquid breaking free from the surface is called evaporation. Also known as vaporization. Evaporation is a physical change in which a substance is converted from its liquid form to its gaseous form. The gaseous form is called a vapor.

Boiling In an open container, as you heat a liquid the average kinetic energy of the molecules increases, giving more molecules enough energy to escape the surface. So the rate of evaporation increases. Eventually, the temperature is high enough for molecules in the interior of the liquid to escape. A phenomenon we call boiling.

The boiling point is the temperature at which the (equilibrium) vapor pressure of a liquid is equal to the external pressure. The normal boiling point is the temperature at which a liquid boils when the external pressure is 1 atm. 12.8

Temperature and Boiling As you heat a liquid, its temperature increases until it reaches its boiling point. Once the liquid starts to boil, the temperature remains the same until it all turns to a gas. All the energy from the heat source is being used to overcome all of the attractive forces in the liquid.

The critical temperature (Tc) is the temperature above which the gas cannot be made to liquefy, no matter how great the applied pressure. The critical pressure (Pc) is the minimum pressure that must be applied to bring about liquefaction at the critical temperature. 12.8

H2O (s) H2O (l) The melting point of a solid or the freezing point of a liquid is the temperature at which the solid and liquid phases coexist in equilibrium Melting Freezing 12.8

Sublimation Sublimation is a physical change in which the solid form changes directly to the gaseous form. Without going through the liquid form. Like melting, sublimation is endothermic.

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A phase diagram summarizes the conditions at which a substance exists as a solid, liquid, or gas. Phase Diagram of Water 12.9

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