Chemical Reactions

What is a chemical reaction? A chemical reaction is the process by which substances undergo change to produce different substances These new substances have different properties from the original substances

Clues to chemical reactions Gas Formation Solid Formation Color change Energy change

Breaking and making bonds New substances are formed in chemical reactions because chemical bonds are broken, atoms rearranged, and new bonds form to form new substances

Chemical formulas Shorthand notation for a chemical compound Includes subscripts – number written below and to the right of the symbol to let you know the number of elements present

Chemical equations Shorthand description of a chemical reaction

Reacts yield products Reactants – starting materials in a chemical reaction Products – substances formed from a reaction Coefficient – number placed in front of a chemical symbol or formula

Type of Reaction Definition A = Red B = Blue C = Green D = Yellow Type of Reaction Definition Equation Synthesis Decomposition Single Replacement Double Replacement Two or more elements or compounds combine to make a more complex substance A + B → AB Compounds break down into simpler substances AB → A + B Occurs when one element replaces another one in a compound AB + C → AC + B AB + CD → AC + BD Occurs when different atoms in two different compounds trade places

Law of Conservation of Mass Mass is neither created nor destroyed in ordinary chemical and physical changes A chemical equation must show the same number and kind of atom on both sides of the arrow

Energy released in exothermic reactions Exo means “exit” and thermic means “heat” or “energy” EXAMPLES: Glow sticks Flashlight Campfire Fireworks

Energy is absorbed in endothermic reactions Endo means “go in” and thermic means “heat” or “energy” Examples Ice pack

Energy is conserved – It's a LAW! Energy can be neither created nor destroyed