1. Unit 5

2. converted A chemical reaction is a change in which one or more substances are converted into new substances element compound Review: a substance is an element or a compound

3. before The reactants are the substances that exist before the reaction after The products are the substances that exist after the reaction

4. equal Law of Conservation of Mass: The total mass of the products must always equal the mass of the reactants Mercury (II) oxide = oxygen + mercury 10.0g = 0.7g + 9.3g

5. formulas symbolscoefficients A chemical equation describes the chemical reaction using formulas and symbols (and usually coefficients) Ca + O 2 → CaO

6. two atoms Seven elements are always written as two atoms bonded together! subscript When writing chemical equations, you will always write these elements with a subscript of a ‘2’ Br 2 I 2 N 2 Cl 2 H 2 O 2 F 2

7. Yields Coefficient Subscript

8. Symbols for State (s) Solids: (s) (l) Liquids: (l) water(aq) Dissolved in water: (aq) (g) Gases: (g) 2 Mg (s) + O 2 (g) → 2 MgO (s)

9. units Coefficients represent the number of units of each substance that take part in the reaction Al + O 2  Al 2 O 3

10. conserved balance Because mass must be conserved, coefficients are used to balance an equation same The same number of atoms of each element must be on both sides of the equation 4 Al + 3 O 2  2 Al 2 O 3

11. Trial and Error Method! Cu + O 2 → Cu 2 O Al + O 2 → Al 2 O 3

12. N 2 + H 2 → NH 3 Mg + P 4 → Mg 3 P 2

13. Al(OH) 3 + HBr  AlBr 3 + HOH

14. NH 4 OH + H 3 PO 4  (NH 4 ) 3 PO 4 + HOH