2. Objectives Write chemical equations to describe chemical reactions Balance chemical equations Classify and identify chemical reactions Predict products from chemical reactions

3. YouTube - ammonium dichromate volcano YouTube - Nitrogen Triiodide Detonation YouTube - Sodium and Water YouTube - Reaction of Sodium & Chlorine (with subtitles) YouTube - Reaction of Sodium & Chlorine (with subtitles)

4. I. Reactions and equations Evidence of a chemical reaction Temperature change Change in color

5. Evidence of chemical change Gas production (bubbles, fizzing) Appearance of a solid (precipitate)

6. Representing chemical reactions: Reactants: starting substances (written on the left side) Products: substances that result from the reaction (written on the right side)

7. Symbols used in chemical equations SymbolMeaning  Yield (placed between reactants and products) +Separate two or more reactants or products (s)Substance is in a solid state (l)Substance is in a liquid state (g)Substance is in a gaseous state (aq)Substance is in an aqueous (water) solution  Heat is applied A substance written above an arrow indicates it is a catalyst needed for the reaction Pt

8. Word equations: indicates the reactants and products in a chemical reaction iron(s) + chlorine (g)  iron (III) chloride (s) “iron and chlorine react to produce iron(III) chloride” Word equations lack important information Skeleton equations Uses chemical formulas to represent reactants and products Fe (s) + Cl 2 (g)  FeCl 3 (s)

9. Practice: Write the skeleton equations for the following: 1. Hydrogen (g) + Bromine (l)  hydrogen bromide (g) 2. Carbon monoxide (g) + oxygen (g)  carbon dioxide (g)

10. Practice: Write the skeleton equations for the following: 1. Hydrogen (g) + Bromine (l)  hydrogen bromide (g) H 2 (g) + Br 2 (l)  HBr (g) 2. Carbon monoxide (g) + oxygen (g)  carbon dioxide (g) CO (g) + O 2 (g)  CO 2 (g)

11. II. Balancing chemical equations Chemical equations: Must obey “law of conservation of matter” Must show that the number of atoms of each substance is the same before and after the reaction. A chemical equation has to be BALANCED To balance chemical equations, COEFFICIENTS (whole number)are written in front of a reactant or product. If coefficient is 1, it is not written

12. Steps for balancing equations 1. Write the skeleton equation for the reaction. Ex. Hydrogen gas reacts with chlorine gas and yields gaseous hydrogen chloride. H 2 (g) + Cl 2 (g)  HCl(g) 2. Count the atoms of each substance for the reactants and products. REACTANTSPRODUCTS H : Cl :

13. 3. Place coefficients (ONLY IN FRONT OF A REACTANT OR PRODUCT) to make number of atoms of each element equal on both sides of the equation. (#atoms= coefficient x subscript) H 2 (g) + Cl 2 (g)  HCl(g) REACTANTSPRODUCTS H : Cl :

14. 4. Write coefficients in lowest ratio possible H 2 (g) + Cl 2 (g)  HCl(g) 5. Check your answer. REACTANTSPRODUCTS H : Cl :

15. Practice 1. Write a balanced chemical equation if magnesium bromide reacts with chlorine and yield magnesium chloride and bromine.

16. 2. Write a balanced chemical equation for: Potassium nitrate  potassium nitrite + oxygen

17. 3. Balance the following reaction CaO + H 2 O  Ca(OH) 2

18. 4. Reactions for gummy bear sacrifice KClO 3  KCl + O 2 C 12 H 22 O 11 + O 2  C + CO 2 + H 2 O