Objectives Relate the properties of a state to the energy content and particle arrangement of that state of matter. Explain forces and energy changes involved in changes of state. Section 1 States and State Changes Chapter 11

States of Matter Most substances can be in three states: solid, liquid, and gas. Solid Particles Have Fixed Positions The particles in a solid are very close together and have an orderly, fixed arrangement. Solid particles can vibrate only in place and do not break away from their fixed positions. Solids have fixed volumes and shapes. Section 1 States and State Changes Chapter 11

 Mercury in Three States Chapter 11 Section 1 States and State Changes

States of Matter, continued Liquid Particles Can Move Easily Past One Another The particles in a liquid are very close together and have a random arrangement. Liquid particles have enough energy to be able to move past each other readily, which allows liquids to flow. Liquids have fixed volumes but can flow to take the shape of the lower part of a container. Section 1 States and State Changes Chapter 11

States of Matter, continued Liquid Forces Lead to Surface Wetting and Capillary Action Liquid particles can have cohesion, attraction for each other. Liquid particles can also have adhesion, attraction for particles of solid surfaces. The balance of cohesion and adhesion determines whether a liquid will wet a solid surface. The forces of adhesion and cohesion will pull water up a narrow glass tube, called a capillary tube. Section 1 States and State Changes Chapter 11

Section 1 States and State Changes Chapter 11

States of Matter, continued Liquids Have Surface Tension Below the surface of a liquid, the particles are pulled equally in all directions by cohesive forces. However, surface particles are pulled only sideways and downward, so they have a net downward force. It takes energy to oppose this net force and increase the surface area. The tendency of liquids to decrease surface area to the smallest size possible is surface tension. Section 1 States and State Changes Chapter 11

Section 1 States and State Changes Chapter 11

States of Matter, continued Gas Particles Are Essentially Independent The particles in a gas are very far apart and have a random arrangement. The attractive forces between particles in a gas do not have a great effect, so the particles move almost independently of one another. The shape, volume, and density of an amount of gas change depending on the size and shape of the container. Section 1 States and State Changes Chapter 11

Section 1 States and State Changes Chapter 11

Changing States Most substances can undergo six changes of state: freezing, melting, evaporation, condensation, sublimation, and deposition. Temperature, Energy, and State Generally, adding energy to a substance will increase the substance’s temperature. But after a certain point, adding more energy will cause a substance to experience a change of state instead of a temperature increase. Section 1 States and State Changes Chapter 11

 Changes of State Section 1 States and State Changes Chapter 11

Changing States, continued Liquid Evaporates to Gas Energy is required to separate liquid particles. They gain energy when they collide with each other. If a particle gains a large amount of energy, it can leave the liquid’s surface and join gas particles. Evaporation is the change of state from liquid to gas. Evaporation is an endothermic process. Boiling point is the temperature and pressure at which a liquid and a gas are in equilibrium. Section 1 States and State Changes Chapter 11

Changing States, continued Gas Condenses to Liquid When gas particles no longer have enough energy to overcome the attractive forces between them, they go into the liquid state. Condensation is the change of state from a gas to a liquid. Condensation is an exothermic process. Condensation can take place on a cool night, causing water vapor in the air to form dew on plants. Section 1 States and State Changes Chapter 11

Visual Concepts Chapter 11

Changing States, continued Solid Melts to Liquid As a solid is heated, the particles vibrate faster and faster in their fixed positions. At a certain temperature, some of the molecules have enough energy to break out of their fixed positions. Melting is the change of state from solid to liquid. Melting is an endothermic process. Melting point is the temperature and pressure at which a solid becomes a liquid. Section 1 States and State Changes Chapter 11

Changing States, continued Liquid Freezes to Solid As a liquid is cooled, the movement of particles becomes slower and slower. At a certain temperature, the particles are pulled together into the fixed positions of the solid state. Freezing is the change of state from a liquid to a solid. Freezing is an exothermic process. Freezing point is the temperature at which a substance freezes. Section 1 States and State Changes Chapter 11

Visual Concepts Chapter 11

Changing States, continued Solid Sublimes to Gas The particles in a solid are constantly vibrating. Some particles have higher energy than others. Particles with high enough energy can escape from the solid. Sublimation is the change of state from solid to gas. Sublimation is an endothermic process. Section 1 States and State Changes Chapter 11

Changing States, continued Gas Deposits to Solid Molecules in the gaseous state become part of the surface of a crystal. When a substance changes state from a gas to a solid, the change is often called deposition. Deposition is an exothermic process. Section 1 States and State Changes Chapter 11