Physical and Chemical Changes Notes

Examples: melting, evaporating, freezing, cutting Page 33 Physical and Chemical Changes Matter can change. The types of changes matter undergoes are classified into two groups: physical changes and chemical changes. A physical change alters the physical properties of a substance without changing the identity of the substance. Physical changes cause a change in properties such as volume, mass, or state of matter. Many physical changes can be reversed. Examples: melting, evaporating, freezing, cutting A chemical change occurs when a substance is changed into a new substance with different properties. During a chemical change, the identity of a substance is changed. Examples: burning, rusting, baking, combusting, reacting

More on Physical Changes Page 35 More on Physical Changes The transformation of matter from one state to another is called a phase transition. Phase transitions are physical changes and occur at precise points when the energy of motion in the atom is too much or too little for the atom to remain at that state. Phase Transition Description Melting (add heat) Solid to Liquid Evaporation (heat added) Liquid to Gas Sublimation (heat added) Solid to Gas (skipping Liquid) Condensation (heat removed) Gas to Liquid Freezing (heat removed) Liquid to Solid Deposition (heat removed) Gas to Solid (skipping Liquid)

On page 34 The following processes are phase transitions. Identify the type of transition. Phase Transition Water droplets coat your cold soda can on a hot day. A cloud releases rain. Solid dry ice steams in air. Glaciers floating in the ocean are shrinking. Morning dew disappears from the grass by midday. A cloud releases snow.

More on Chemical Changes Page 37 More on Chemical Changes A chemical reaction is the process by which new substances are formed during a chemical change. Some signs that indicate a chemical reaction has occurred include the bubbling, fizzing, turns cloudy, forming of gases, a change in color, the release of heat, the emission of light, heats up (exothermic) release of energy or cools off (endothermic) takes in energy Another sign of a chemical reaction is the formation of a precipitate. A precipitate is a solid that forms from a chemical reaction that takes place in a solution. It is very difficult or impossible to reverse the effects of a chemical change.

Iron rusts sodium hydroxide dissolves in water milk goes sour page 32 Create a two-column table and classify each of the descriptions below as either a physical change or a chemical change. Iron rusts sodium hydroxide dissolves in water milk goes sour a match ignites and burns an ice cube melts to form a puddle of water icicles form at the edge of a roof chocolate bar melts in the sun water is heated and changed into steam vinegar and baking soda react acid on limestone produces carbon dioxide gas wood and leaves rot a tea kettle begins to whistle Physical Change Chemical Change

PHYSICAL OR CHEMICAL CHANGE? YES PHYSICAL CHANGE NO CHEMICAL CHANGE QUESTION: AFTER THE CHANGE IS IT THE SAME SUBSTANCE? EVIDENCE OF A CHEMICAL CHANGE BUBBLING TURNS CLOUDY TEMPERATURE CHANGES EXOTHERMIC – ENERGY IS EXITING - GETS HOTTER ENDOTHERMIC – ENERGY IS ENTERING – GETS COOLER COLOR CHANGE CHANGE IN SMELL OR TASTE