14:1 Forming New Substances Chemical Reactions 14:1 Forming New Substances

Terms Chemical reaction Chemical formula Chemical equation Reactants Products Law of conservation of mass

Clues to Chemical Reactions Gas formation Look for bubbles Solid formation Precipitate: a solid formed in a solution Color change Energy change Release or absorption of energy

Breaking and Making Bonds Reaction of Hydrogen and Chlorine

Chemical Formulas Tells how many of each atom is in a molecule H2O C6H12O6 C14H9Cl5 C3H5N3O9 C3H8O

Chemical Formulas Atoms in parentheses: multiply everything inside the parentheses by the subscript number. Ca(NO3)2 Mg(OH)2 Al2(SO4)3

Chemical Equations Reactants yield product Atoms are not lost or gained Number of atoms in the reactants is equal to the number of atoms in the products Law of conservation of mass is the reason

Chemical Equations

Types of Chemical Reactions

Synthesis Reactions Reaction in which two or more substances combine to form a single compound

Decomposition Reactions Reaction in which a single compound breaks down to form two or more simpler substances

Single Replacement Reactions Reaction in which an element takes the place of another element that is part of a compound.

Double Replacement Reactions Reaction in which ions in two compounds switch places

Energy and Rates of Chemical Reactions

Every Reaction Involves Energy Exothermic-Energy is released (gives energy to the surroundings) “exo”- exit “thermic”- heat or energy Light energy is released in glow sticks Light and thermal energy released in campfire

Every Reaction Involves Energy Endothermic-Energy is absorbed “endo”- go in “thermic”- heat or energy Activation Energy Minimum amount of energy needed for substances to react

Every Reaction Involves Energy

Factors Affecting Rates of Reactions Temperature Increase in temperature increase in rate of reaction Concentration (density)-amount of one substance dissolved in another Increase in concentration increase in rate of reaction Surface Area Increase in surface area increase in rate of reaction Catalysts and Inhibitors Catalyst- substance that speeds up rate of reaction without being permanently changed (enzymes in body) Inhibitor-substance that slows down or stops a chemical reaction (food preservatives)