PHASE CHANGES

Phases Changes in Matter: (Also examples of Physical Changes) 1. Melting 2. Freezing 3. Vaporization 4. Condensation 5. Sublimation Physical Change: a substance changes from one form to another, but it remains the same kind of substance. No new matter is formed.

Solid-Liquid Phase Changes Melting: the change of a solid to a Melting: the change of a solid to a liquid. liquid. 1. Occurs when a substance absorbs heat energy. heat energy. 2. The crystal structure of the particles breaks down, allowing the particles to breaks down, allowing the particles to flow freely around one another. flow freely around one another. Melting-point: the temperature at which a Melting-point: the temperature at which a solid changes to a liquid. (Ice melts at 0°C) solid changes to a liquid. (Ice melts at 0°C)

Melting

Liquid-Solid Phase Changes Freezing: the change of a liquid into a solid. Freezing: the change of a liquid into a solid. 1. occurs when a substance loses heat energy. Freezing-point: the temperature at which a substance Freezing-point: the temperature at which a substance changes from a liquid to a solid. changes from a liquid to a solid. 1. The freezing point of a substance is equal to its melting point. ( ice melts at 0°C and water melting point. ( ice melts at 0°C and water freezes at 0°C) freezes at 0°C) Alcohols: have freezing points much lower than 0°C. Alcohols: have freezing points much lower than 0°C. 1. Used in automobile antifreeze. 2. Even the coldest winter temperatures will not cause the water in the radiator to freeze. cause the water in the radiator to freeze.

Freezing

Liquid-Gas Phase Changes Vaporization: the change of a substance from a Vaporization: the change of a substance from a liquid to a gas. liquid to a gas. 1. Particles in a liquid absorb enough 1. Particles in a liquid absorb enough heat energy to escape from the heat energy to escape from the liquid phase. liquid phase. Evaporation: if vaporization takes place at the Evaporation: if vaporization takes place at the surface of the liquid. surface of the liquid. Condensation: if a substance in the gas phase Condensation: if a substance in the gas phase loses heat energy, it changes into a loses heat energy, it changes into a liquid. liquid. Example: 1) a cold glass iced drink tends to Example: 1) a cold glass iced drink tends to become wet on the outside. This is become wet on the outside. This is because water vapor condenses. because water vapor condenses. 2) Rain 2) Rain

Condensation

Liquid-Gas Phase Changes C. Boiling: particles inside a liquid change to gas, and then the particles travel to the surface of the then the particles travel to the surface of the liquid and into the air. liquid and into the air. D. Boiling-point: the temperature at which a liquid boils. Water boils at 100°C. Water boils at 100°C. 1. Related to the pressure of the air above it. a. the lower the air pressure ( the less the “push” of the air pressing down), the more “push” of the air pressing down), the more easily the bubbles of gas can form within easily the bubbles of gas can form within the liquid and then escape. the liquid and then escape. Lowering the air pressure lowers the boiling point. Lowering the air pressure lowers the boiling point. b. at high altitudes the air pressure is much lower, so you would be able to boil water at lower, so you would be able to boil water at ordinary room temperature. ordinary room temperature.

Solid-Gas Phase Changes Sublimation: when a substance’s Sublimation: when a substance’s surface particles escape surface particles escape directly into the gas directly into the gas phase. They do not phase. They do not pass through the liquid pass through the liquid phase. phase. Example: Dry Ice Example: Dry Ice

Sublimation Dry Ice

Deposition: Gas to Solid When water vapor in air loses so much energy it turns directly into a solid. When water vapor in air loses so much energy it turns directly into a solid. Frost! Frost!

Energy in Phase Change DEPOSITION

More About the Phase Changes Earth is known as the “water” planet. Earth is known as the “water” planet. 1. ¾ of the Earth’s surface is water 1. ¾ of the Earth’s surface is water 2. 1% of the Earth’s atmosphere exists in 3 phases 2. 1% of the Earth’s atmosphere exists in 3 phases a. Ice a. Ice b. Liquid water b. Liquid water c. Water vapor c. Water vapor A solid substance has less energy than the same substance in the liquid phase. A solid substance has less energy than the same substance in the liquid phase. A gas usually has more energy than the liquid phase of the same substance. A gas usually has more energy than the liquid phase of the same substance. Ice has less energy than liquid water. Ice has less energy than liquid water. Steam has more energy than ice or liquid water. Steam has more energy than ice or liquid water.

More About the Phase Changes Because energy content is responsible for the different phases of matter, substances can be made to change phase by adding or taking away energy. Because energy content is responsible for the different phases of matter, substances can be made to change phase by adding or taking away energy. *The easiest way to do this is to heat or cool the *The easiest way to do this is to heat or cool the substance. substance. Examples: 1) Liquid water is put into freezer to remove heat and make ice. heat and make ice. 2) On a stove you add heat to make liquid 2) On a stove you add heat to make liquid water turn to steam. water turn to steam. Physical Change: a substance changes from one form to another, but it remains the same kind of substance. No new it remains the same kind of substance. No new matter is formed. matter is formed.

Chemical Properties/Changes Chemical Properties: The properties that describe how a substance changes into other new substances. Example: The ability of a substance to burn. 1. Flammability: The ability to burn. (Hydrogen) 2. Supporting-Burning (Oxygen) Chemical Changes: The changes that substances undergo when they turn into other substances. Example: The process of burning.

Chemical Properties/Changes A Chemical Property describes a substance’s ability to change into a different substance; A Chemical Change is the process by which the substance changes. Chemical Reaction: (another name for a chemical change) The process in which the physical and chemical properties of the original substance change as a new substance with different physical and chemical properties is formed.