1. Chemical Reactions Balancing and Classifying Chemical Equations

2. Chemical Reactions Chemical reactions occur when a chemical change occurs Chemical reactions occur when a chemical change occurs

3. Evidence of a Chemical Reaction Color change Color change Formation of a gas Formation of a gas Odor change Odor change Formation of a precipitate Formation of a precipitate Temperature change Temperature change pH change pH change

4. Why do chemical reactions occur? Chemical reactions occur because the products are more stable than the reactants. Chemical reactions occur because the products are more stable than the reactants. All substances react in an effort to become more stable. All substances react in an effort to become more stable.

5. Common Symbols in Chemical Equations

6. Reactants and Products Reactants (ingredients) -> Products Reactants (ingredients) -> Products

7. How many oxygen atoms are in the reactants? How many oxygen atoms are in the reactants? How many oxygen atoms are in the products? How many oxygen atoms are in the products?

8. Balancing Equations

9. Law of Conservation of Matter (or mass): Law of Conservation of Matter (or mass): In a chemical reaction, matter can be neither created nor destroyed. In a chemical reaction, matter can be neither created nor destroyed. In a chemical reaction, the amount of reactants equal the amount of products. In a chemical reaction, the amount of reactants equal the amount of products.

10. Balancing Equations Paraphrase: Paraphrase: Law of Conservation of Atoms: Law of Conservation of Atoms: The number of atoms of each type of element must be the same on each side of the equation. The number of atoms of each type of element must be the same on each side of the equation.

11. Balancing Equations Hydrogen and oxygen are diatomic elements. Their subscripts cannot be changed. The subscripts on water cannot be changed. Hydrogen + oxygen water Hydrogen + oxygen water H 2 + O 2 H 2 O H 2 + O 2 H 2 O

12. Balancing Equation Count the atoms on each side. Reactant side: 2 atoms H and 2 atoms O Product side: 2 atoms H and 1 atom O H 2 + O 2 H 2 O H 2 + O 2 H 2 O

13. Balancing Equations H 2 + O 2 H 2 O H 2 + O 2 H 2 O If the subscripts cannot be altered, how can the atoms be made equal? If the subscripts cannot be altered, how can the atoms be made equal? Adjust the number of molecules by changing the coefficients. Adjust the number of molecules by changing the coefficients.

14. Balancing Equations Reactants: 2 atoms of H and 2 atoms of O Products: 4 atoms of H and 2 atoms of O H is no longer balanced! H 2 + O 2 2H 2 O H 2 + O 2 2H 2 O

15. Balancing Equations Reactant side: 4 atoms of H and 2 atoms of O Product side: 4 atoms of H and 2 atoms of O It’s Balanced! 2H 2 + O 2 2H 2 O 2H 2 + O 2 2H 2 O

16. Balancing Equations 2H 2 + O 2 2H 2 O 2H 2 + O 2 2H 2 O

17. Balancing Equations Balancing hints: Balancing hints: Count all atoms and polyatomic ions occurring on each side of -> Count all atoms and polyatomic ions occurring on each side of -> Balance the metals first. Balance the metals first. Balance the polyatomic ions next. Balance the polyatomic ions next. Balance the other atoms. Balance the other atoms. Save the oxygen and hydrogen until the end. Save the oxygen and hydrogen until the end.

18. Diatomic elements – always exist in pairs Remember the diatomic elements: H 2, N 2, O 2, F 2, Cl 2, Br 2, and I 2. Remember the diatomic elements: H 2, N 2, O 2, F 2, Cl 2, Br 2, and I 2.

19. Types of Reactions 1. Synthesis (or Addition or Combination) Reactions 1. Synthesis (or Addition or Combination) Reactions A + B AB  2 or more substances combine to form a new compound. (A and B are elements or compounds)  small molecules join to form chains - polymerization Fe + O 2 Fe 2 O 3

20. Types of Reactions 2. Decomposition Reactions 2. Decomposition Reactions ABA + B ABA + B  compounds are broken apart into smaller substances Example: Electrolysis of water 2 H 2 O 2 H 2 + O 2 2 H 2 O 2 H 2 + O 2

21. Types of Reactions Single – Replacement Reaction Single – Replacement Reaction AX + BBX + A AX + BBX + A  One element replaces a similar element in a compound  Fe + CuCl 2 FeCl 2 + Cu  Look at the Metals activity series

22. Types of Reactions Double – Replacement Reaction Double – Replacement Reaction AX + BYAY + BX  Ions from 2 compounds in solution exchange places to produce 2 new compounds.  One of the compounds is usually …  A precipitate  A gas that bubbles off  A molecular compound like water

23. Types of Reactions Combustion Reactions Combustion Reactions These use O 2 as a reactant These use O 2 as a reactant One product contains O, usually H 2 O One product contains O, usually H 2 O____________________________________________________________________________________________________________________________ Importance of Good Air Supply 2CH 4 + 4O 2 2CO 2 + 4H 2 O 2CH 4 + 3O 2 2CO + 4H 2 O 2CH 4 + 2O 2 2C + 4H 2 O

24. 24 Some Metals in the Activity Series