1. Chemical Reactions 8th Grade Science 2012

2. Physical Properties - Review Color Shape Mass State of Matter Length Magnetism

3.  Cutting a steak  Cracking an egg  Chopping wood  Bending metal EXAMPLES  Tearing Paper Physical Changes

4. Chemical Changes  Burning wood  Frying an egg  Digesting a steak  Rusting of metal result of a Chemical Reaction

5. New color New odor Gas bubbles Light production An increase or decrease in temperature Chemical Change occurs when…

6. Chemists use chemical formulas to describe chemical reactions: Chemists use chemical formulas to describe chemical reactions: Reactant + Reactant YIELDS (makes, produces) English: Sulfur dioxide plus oxygen yields sulfer trioxide Product

7. All chemical reactions have two parts: Reactants - the substances you start with Reactants - the substances you start with Products- the substances you end up with (new substances are formed) Products- the substances you end up with (new substances are formed) The reactants turn into the products. The reactants turn into the products. Reactants  Products

8. Balanced Equation Atoms can’t be created or destroyed – Law of Conservation of Mass Atoms can’t be created or destroyed – Law of Conservation of Mass All the atoms we start with we must end up with All the atoms we start with we must end up with A balanced equation has the same number of each element on both sides of the equation. Atoms are rearranged. A balanced equation has the same number of each element on both sides of the equation. Atoms are rearranged.

9. Chemical Equations NaOH + HCl -------> H 2 O + NaCl Which is the reactant? product? Which is the reactant? product? Count the atoms on the reactant side. Count the atoms on the reactant side. Count the atoms on the product side. Count the atoms on the product side. Is it even? Is it even?

10. Coefficients & Subscripts Subscript number – number of atoms in a molecule Coefficient – the number of molecules

11. When you count atoms, remember to multiply the coefficient number and the subscript number. When you count atoms, remember to multiply the coefficient number and the subscript number.Practice: 2H 2 O 2H 2 O 2(NaOH) 4 2(NaOH) 4

12. Practice counting atoms: CH 4 + O 2  CO 2 + H 2 O CH 4 + O 2  CO 2 + H 2 O CH 4 + O 2  CO 2 + 2H 2 O CH 4 + O 2  CO 2 + 2H 2 O CH 4 +5O 2  CO 2 + 2H 2 O + 3O 2 CH 4 +5O 2  CO 2 + 2H 2 O + 3O 2

13. Examples AgNO 3 + Cu  Cu(NO 3 ) 2 + Ag AgNO 3 + Cu  Cu(NO 3 ) 2 + Ag Mg + N 2  Mg 3 N 2 Mg + N 2  Mg 3 N 2 P + O 2  P 4 O 10 P + O 2  P 4 O 10 Na + H 2 O  H 2 + NaOH Na + H 2 O  H 2 + NaOH CH 4 + O 2  CO 2 + H 2 O CH 4 + O 2  CO 2 + H 2 O