Chemical Reactions
What is a chemical reaction? A chemical reaction is the process by which substances undergo change to produce different substances, with different properties 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 Equation Synthesis Decomposition Single Replacement Double Replacement A = Red B = Blue C = Green D = Yellow A + B → AB AB → A + B AB + C → AC + B AB + CD → AC + BD Two or more elements or compounds combine to make a more complex substance Compounds break down into simpler substances Occurs when one element replaces another one in a compound 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 Balancing Equations
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! Law of Conservation of Energy Energy can be neither created nor destroyed