1. Chemical Reactions

2. Know the difference: physical or chemical? Physical Changes form, shape, phase but not what it is Cutting, grinding, molding, breaking Melting, freezing, evaporating, condensing Mixing (salt in water, gas in water such as carbonation) In some cases, reversible Chemical Chemical bonds are broken and atoms are rearranged Burning, rusting, baking, hydrolyzing New substance forms Not reversible

3. Signs a chemical reaction has occurred Change in temperature Exothermic – energy released, feels hot Endothermic – energy absorbed, feels cold Change in color Not sure sign, because color can change in physical mixing Light produced Gas produced (odor or bubbles) Formation of a precipitate (solid formed when two liquids are mixed) http://www.youtube.com/watch?v=FOeH29hlHlU http://www.kentchemistry.com/links/Matter/PhysicalChemicalChanges.htm

4. Tests for gases produced Read how to test for oxygen, hydrogen, and carbon dioxide http://chemstuff.co.uk/analytical-chemistry/tests-for-gases/

5. A few examples… Leaves changing color Fireworks (remember flame colors specific to elements?) Sodium and chlorine combine to form sodium chloride 2 Na (s) + Cl 2 (g)  2 NaCl (s)

6. Writing chemical equations A few notes Reactants on left Reactants = what goes into the reaction Products on right Products = what comes out of the reaction Arrow means yield  Symbols for state of matter (s, l, g, aq) Solid, liquid, gas, aqueous (in solution) Formulas must be written correctly Diatomic elements: H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2 NH 3 = ammonia

7. Recognize Acids and Bases Acids Include hydrogen ions HCl – hydrochloric H 2 SO 4 – sulfuric HNO 3 – nitric CH 3 COOH – acetic H 3 PO 4 – Phosphoric H 2 CO 3 -Carbonic Bases Include hydroxide ion combined with a metal NaOH – sodium hydroxide Ca(OH) 2 – calcium hydroxide

8. Try writing these out! 1.Nitrogen plus hydrogen yield ammonia 2.Solid sodium chloride breaks down to solid sodium and chlorine gas. 3.Solid Iron in a lead (II) sulfate solution react forming iron (II) sulfate solution plus solid lead. 4.Potassium chloride and zinc phosphate react to form zinc chloride and potassium phosphate 5.Carbon tetrahydride and oxygen combust to form carbon dioxide and water. 6.Aqueous hydrochloric acid and aqueous sodium hydroxide react to form aqueous sodium chloride and water.

9. Nitrogen plus hydrogen yield ammonia N 2 + H 2  NH 3 Reaction type: Synthesis How to tell: two reactants combine to form one product Questions to ponder: Why are nitrogen and hydrogen written with a 2 subscript?

10. Solid sodium chloride breaks down to solid sodium and chlorine gas NaCl (s)  Na (s) + Cl 2 (g) Reaction type: decomposition How to tell: one reactant is broken into two or more parts Questions to ponder: How does 1 chlorine atoms go into the reaction but there are 2 atoms of chlorine produced?

11. Solid Iron in a lead (II) sulfate solution react forming iron (II) sulfate solution plus solid lead Fe (s) + PbSO 4 (aq)  FeSO 4 (aq) + Pb (s) Reaction type: Single replacement How to tell: one single element replaces another element in a compound Think of PbSO 4 as a couple dancing – Pb +2 and SO 4 -2. Along comes Fe and SO 4 -2 decides to get a new partner, leaving Pb +2 all alone!

12. Potassium chloride and zinc phosphate react to form zinc chloride and potassium phosphate KCl + Zn 3 (PO 4 ) 2  ZnCl 2 + K 3 PO 4 Reaction type: double replacement How to tell: two compounds react and the cations switch places, producing two compounds In this case, there are two pairs of dancers. Potassium and zinc switch partners. NOTE: symbols, charge, cross and reduce on BOTH sides of the equation How do you know the charge on zinc?

13. Carbon tetrahydride and oxygen combust to form carbon dioxide and water CH 4 + O 2  CO 2 + H 2 O Reaction type: combustion How to tell: always carbon source and oxygen in with CO 2 + H 2 O produced Don’t confuse with a double replacement! Even though there are compounds on both sides, they are not just switching partners.

14. Aqueous hydrochloric acid and aqueous sodium hydroxide react to form aqueous sodium chloride and water HCl (aq) + NaOH (aq)  NaCl (aq) + H 2 O Reaction type: Acid base neutralization How to tell: Acid and base react to form salt (ionic compound) and water Again, looks like a double replacement but is a specific type.

15. Types of Chemical Reactions Summary Synthesis – 2 reactants  1 product Decomposition – 1 reactant  2 products Single replacement – single element on both sides Double replacement – all elements paired Combustion – carbon + O 2  CO 2 + H 2 O Acid-base – acid + base  salt + H 2 O

16. You try it. Identify each reaction type. List what type the following reactions are: 1) NaOH + KNO 3 --> NaNO 3 + KOH 2) CH 4 + 2 O 2 --> CO 2 + 2 H 2 O 3) 2 Fe + 6 NaBr --> 2 FeBr 3 + 6 Na 4) CaSO 4 + Mg(OH) 2 --> Ca(OH) 2 + MgSO 4 5) NH 4 OH + HBr --> H 2 O + NH 4 Br 6) Pb + O 2 --> PbO 2 7) Na 2 CO 3 --> Na 2 O + CO 2

17. Law of Conservation of Mass What is the law of conservation of mass? Cannot create or destroy matter, only rearrange Mass in = mass out Which reminds us, how can more atoms come out of a reaction than go in? Answer: They can’t!!!

18. Balancing Chemical Equation Based on the law of conservation of mass, the atoms of reactant that go into a reaction must equal the atoms of products that come out This is accomplished using COEFFICIENTS! Coefficients are large numbers in front of compounds that change the number of molecules

19. Rules for Balancing Equations Only coefficients can be changed The  acts as an = The atoms on the left equal the atoms on the right Trial and error Use lowest coefficients possible See if you can balance this: ____N 2 + ____H 2  ___NH 3

20. N 2 + 3 H 2  2NH 3 There are 2 nitrogen atoms on each side There are 6 hydrogen atoms on each side

21. Use these two sites to review http://www.wfu.edu/~ylwong/balanceeq/balanceq.html http://education.jlab.org/elementbalancing/index.html