1. Chemical Changes

2. Chemical Reactions A change in which one or more substances are changed into new substances Chemical equations have two parts Reactants – substances that react Products – new substances that are formed or produced Reactants  Products

4. Symbols of Chemical Reactions SymbolMeaning  Produce or forms +Plus (s)Solid (l)Liquid (g)Gas (aq)Aqeuous Heat/Light/Electricity  The reactants re heated/lighted/ or given electrocoty

5. Law of Conservation of Mass The total mass of the products always equals the total mass of the reactants Mass is neither created or destroyed, only transferred

7. Chemical Equations Shorthand way to describe a chemical reaction using chemical formulas and other symbols Example: Hydrogen gas plus oxygen gas produces liquid dihydrogen monoxide H 2 (g) + O 2 (g)  H 2 O (l)

8. Balancing Chemical Equations Coefficients represent the number of units of each substance taking part in a reaction Allow chemists to add the correct amounts of reactants to a reaction and tells them exactly how much product will form Balancing an equation does not change what happens in a reaction, only changes the way the reaction is represented

9. Balancing Chemical Equations A balanced chemical equation is an equation in which the same number of atoms each element on both sides of the equation Trial and error

10. Balancing Chemical Equations 1. Write a chemical equation for the reaction using formulas and symbols. 2. Count the atoms in reactants and products. 3. Choose coefficients that balance the equation. Never change subscripts of a correct formula to balance an equation. 4. Recheck the numbers of each atom on each side of the equation and fix coefficients again if necessary.