Notes:Color Guide

1. Notes:Color Guide • Gold: Important concept. Write this down. • Orange: Definition. Write this down. • Blue: Important information, but you do not need to copy. • Red: Example. Copy if needed. • White: General Discussion (Don’t Copy)

2. + Chapter 6: Chemical Reactions  • Color Change • Bubbling/Smoking • Heat Release / Glowing Section 1: Forming Compounds

3. Definition: chemical reaction – the process that causes a substance to change into a new substance. • Chemical reactions cause atoms to REARRANGE. • One example of a chemical reaction occurs when cations join with anions. Na1+ Cl1- Chemical Reaction

4. Ionic compounds form when cations and anions bond together. • When ionic compounds form, the new compound must have no charge. In other words, all of the + and - charges must cancel out. Na1+ Cl1- Charged Charged Neutral! NaCl

5. Each cation and anion has it’s own charge. Lets look at the cations first. Please copy into your notes. Use only the element symbols.

6. And now for the anions: • When a nonmetal becomes an anion, it’s name changes. • Example: Fluorine  Fluoride • Example: Oxygen  Oxide

7. Na1+ In order to form the new compound, the anions and cations must cancel each other’s charg. Cl1- NaCl What happens if the charges DON’T cancel out??? Na1+ O2- ???

8. To make Sodium Oxide, there must be enough Sodium Cations to balance the Oxygen Anion. Na1+O2- Na1+ Na2O1 Why don’t we add another sodium cation to the reaction? It took 2 Sodium to balance the 1 Oxide.

9. Lets try another one. How about MagnesiumChloride? • This stuff is actually pretty easy… Mg2+Cl1- Cl1- Mg1Cl2 It took 2 Chloride to balance the 1 Magnesium.

10. Try these on your own: • AluminumBromide • AlBr3 • CalciumNitride • Ca3N2

11. One more thing to remember…the metal always comes first. It keeps its original name. The nonmetal comes second. It changes it’s name. Easy!

12. Covalent compounds are named based on the number of atoms they contain. • Prefixes are used to represent the number of atoms. The Prefixes Are: • Rules: • If the first element has only one atom, it gets no prefix. • The first element uses it’s original name.

13. CO2 Examples: • Carbon Di-oxide  • Di-Hydrogen Di-oxide  • Sulfur Tetra-Chloride  H2O2 SCl4

15. Chapter 6: Chemical Reactions Section 2: The Nature of Chemical Reactions

16. There are often signs that a chemical reaction is taking place: • Color Change • Gas Production (bubbling) • Energy Transfer (getting hot or cold, glowing) • These signs indicate that something is being changed & new substancesare forming.

17. So, in a chemical reaction…things REACT to PRODUCE other things. • Definition: reactants – the substances in a chemical reaction that are changed. • Definition: products - the NEW substances produced in a chemical reaction. • The product must contain the same elementsas the reactant.

18. Hydrogen Carbon Oxygen O2 C8H18 + H2O CO2 + Carbon Hydrogen Oxygen During a chemical reaction, atoms are rearranged.

19. Lets look at the reaction of gasoline and oxygen again… • It would be far to dangerous to use gasoline as a fuel if it immediately reacted with oxygen, right? • What do we need in order to start the reaction? A SPARK!

20. Some chemical reactions need energy in order to begin. • Energy breaks the atomic bondsand allows the atoms to rearrange. • Once the bonds are broken, the reactants rearrange into the products. BAM!

21. Perhaps the most important rule in chemistry is: • Definition: Law of Conservation of Mass – states that “In a chemical reaction, mass is never created or destroyed.” • In other words, you MUST have the same number of atoms in the reactant as you have in the product.

22. Some reactions release energy as they occur… • Definition: exothermic change – a physical or chemical change that releases energy. • Exo. changes make the air warmer or give off light (or both). • Examples: combustion and condensation

23. Some reactions absorb energy as they occur… • Definition: endothermic change – a physical or chemical change that absorbs energy. • Endo reactions lower the temp. • Examples: evaporation

24. Chapter 6: Chemical Reactions Section 3: Types of Reactions

25. Definition: chemical equation – a representation of a chemical reaction using element symbols. • The means “yields” or “produces”. Chemical reactions are classified based on what happens to the reactants. Some reactions break the reactants apart… Others causes them to join together. Others just make them change places.

26. When things combine together in a chemical reaction, we call it “synthesis”. • Definition: synthesis reaction – a reaction in which two or more substances combine. • The general formula is: • A + B  AB Na + Cl NaCl H2 + O2 H2O H2 + N2 NH3

27. A and B represent the reactants… • AB represents the product. A + B  AB H2 + N2 NH3 Na + Cl NaCl H2 + O2 H2O

28. When a chemical reaction breaks substances apart, it is called “decomposition”. • Definition: decomposition reaction –a reaction in whicha compound breaks down into simpler substances. The general formula is: AB A+B

29. AB represents the reactant. • A + B represent the products. AB  A + B H2O  H2 + O2 Cl2O5 Cl2 + O2 SO3 SO2 + O3

30. In replacement reactions, substances change places. • Definition: single replacement reaction – a reaction in which one element takes place of another to form a new compound. • The general formula is: • AX + B  BX + A

31. AX +B  BX + A Cl2 + KBr KCl + Br2 Al + Fe2O3 Al2 O3 + Fe

32. Definition: Double Replacement reaction – a reaction in which two elements trade places. • The general formula is: • AX + BY  AY + BX Notice that X takes the place of Y and Y takes the place of X.

33. Definition: combustion reaction – an exothermic reaction in which oxygen is (usually) a reactant. • Combustion reactions often produce H2O and CO2 as products.