Lesson 9 Chemical Reactions

1. Lesson 9 Chemical Reactions Anything in black letters = write it in your notes (‘knowts’)

2. Quick Review… Write the chemical formula for sodium carbonate Na+1 CO3-2 sodium ion carbonate ion CO3 Na 2

3. Section 1 – Counting Atoms Coefficient 2 Na2CO3 Subscripts

4. Subscripts represent the number of atoms in a compound.

5. Coefficients represent the number of each element or compound

6. Section 2 – Balancing Chemical Equations Chemical equations represent chemical reactions Reactants  Products Reactant mass = Product mass # reactant atoms = # product atoms Chemical equations must be balanced to obey the LAW!

7. Word Equations “Sodium carbonate reacts with calcium chloride to produce sodium chloride and calcium carbonate” Chemical Equations Na2CO3 + CaCl2 NaCl + CaCO3 This is NOT balanced

8. 2 Na2CO3 + CaCl2 NaCl + CaCO3 subscripts coefficient When balancing equations, never change subscripts. Instead, add coefficients

9. When balancing equations, never change subscripts. Instead, add coefficients H2 + O2 → H2O 2 2 Al + F2 → AlF3 2 3 2 NaClO3 → NaCl + O2 2 2 3

10. Pt Δ heat More on Chemical Equations or Catalyst – substance that speeds up a chem. rxn but is not part of the chem. equation

11. Balancing Equations Help… 1. Balance 1 element at a time, from left to right. 2. Treat any polyatomic ions as single units if they are on both sides of the reaction. Zn(OH) 2 + H3PO4→ Zn3(PO4)2 + H2O 3 2 6 (OH) is NOT on both sides There is a (PO4) on each side

12. Balancing Equations Hints… • Odd # atoms → even # atoms; multiply through by 2 4 2 CH3OH + O2→ CO2 + H2O 3 2 2 4. Balance oxygen last, it just helps sometimes. 5. Remember, N2, O2, F2, Cl2, Br2, I2, H2

13. Quiz #1 Balance the following chemical equations 1. FeCl3 + H2S → FeCl2 + HCl + S 2. MnO2 + HCl → MnCl2 + H2O + Cl2 3. Hydrochloric acid reacts with solid sodium hydrogen carbonate. The products formed are aqueous sodium chloride, water, and carbon dioxide gas. Write a skeleton equation for this chemical reaction.

14. Section 3 – Types of Chemical Equations Most chemical rxns will fit into 1 of 5 types. • Combination (Synthesis) • Decomposition • Single Replacement • Double Replacement • Combustion

15. Combination • A + B → AB Magnesium metal and oxygen gas combine to form the compound magnesium oxide. 2Mg(s) + O2 (g) → 2 MgO(s)

16. heat • 2. Decomposition • AB → A + B 2HgO(s) 2Hg(l) + O2(g)

17. 3. Single Replacement • A + BC → AB + C • 2K(s) + 2H2O(l) → 2KOH(aq) + H2(g)

18. 4. Double Replacement • AB + CD → AC + BD

19. 5. Combustion • A substance reacts with oxygen (O2) and releases energy • If the substance is a hydrocarbon, then CO2 and H2O are products,

20. CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)

21. Which type of reaction? H2OH2(g) + O2(g) electricity K2CO3(aq) + BaCl2(aq) → 2KCl(aq) + BaCO3(s) 2KI(aq) + Pb(NO3)2(aq) → PbI2 + 2KNO3(aq) 2Fe(s) + 3S(g) → Fe2S3(s) • 2NaN3(s) → 2Na(s) + 3N2(g) • 2K(s) + Cl2(g) → 2KCl(s) S(s) + O2(g) → SO2(g)

22. Zn(s) + Cu(NO3)2(aq) → Cu(s) + Zn(NO3)2(aq) 2C8H18(l) + 25O2(g) → 16CO2(g) + 18H2O(g) Cl2(aq) + 2NaBr(aq) → 2NaCl(aq) + Br2(aq) 2Mg(s) + O2(g) → 2MgO(s) Cu(s) + S(s) → CuS(s)

23. Can you balance these? a) Al + F2→ AlF3 b) C3H8 + O2→ CO2 + H2O c)FeSO4 + Ba(OH)2→ Fe(OH)2 + BaSO4 d) NaClO3→ NaCl + O2

24. Section 4 – Writing Chemical Equations Common acids: H2SO4 – sulfuric acid HCl – hydrochloric acid HNO3 – nitric acid Diatomic Molecules: H2, N2, O2, F2, Cl2, Br2, I2

25. If the substance combusting is a hydrocarbon, then CO2 and H2O are products. Write a balanced chemical equation for the combustion of propane (C3H8).

26. Write a balanced chemical equation for the combination of hydrogen gas and oxygen gas to form water.  Write a balanced chemical reaction for the decomposition of copper(II) hydroxide into copper(II) oxide and water.  

27. Write a balanced chemical equation for the double replacement reaction of sodium nitrate with calcium chloride.  Write a balanced chemical equation for the single replacement reaction of sodium metal with water to form sodium hydroxide and hydrogen gas.

28. Exploratory info for next chapters… What does a coefficient mean? 4 Ag + O2 → Ag2O 2 _____ atoms of Ag will react with _____ molecule(s) of O2 to form _____ formula units of Ag2O A coefficient represents the combining ratio of reactants & products in a chemical rxn.

29. Exploratory info for next chapters… 4 Ag + O2 → Ag2O 2 1. How many molecules of oxygen (O2) would be needed to react with 4 atoms of silver? 2. How many molecules of oxygen (O2) would be needed to react with 8 atoms of silver? 3. How many formula units of silver oxide would be formed in 1? In 2?

30. Exploratory info for next chapters… 4 Ag + O2 → Ag2O 2 How many oxygen molecules would be needed to form 20 formula units of silver oxide? How many atoms of silver would be required as well?

31. Exploratory info for next chapters… 4 Ag + O2 → Ag2O 2 If 20 atoms of silver react with 20 molecules of oxygen, which reactant would be used up completely? Which reactant would be leftover? How many formula units of silver oxide would be formed?

32. Exploratory info for next chapters… Limiting Reactant - Reactant that is completely used up; limits the amount of product that can be produced. Excess Reactant - Reactant that remains un-reacted; is not completely used up.

33. Exploratory info for next chapters… Fe2O3 + CO → Fe + CO2 3 2 3 1. How many molecules of CO are needed to produce 4 atoms of Fe? 6 CO molecules 2. How much Fe2O3 is assumed to be present in the question above? Assuming that there is at least 2 formula units of Fe2O3