Balancing Reactions

1. Balancing Reactions --for unbalanced students

2. Write the reaction • Butane gas(C4H10) burns in oxygen gas to form carbon dioxide gas and water vapor

3. Write the reaction • Butane gas(C4H10) burns in oxygen gas to form carbon dioxide gas and water vapor C4H10(g) + O2(g)  CO2(g) + H2O(g) “forms” “and”

4. Write the reaction • Aqueous sodium bromide and chlorine gas form aqueous sodium chloride and liquid bromine • Silver (I) oxide decomposes to form solid silver and oxygen gas • Solid phosphorus burns in oxygen gas to form diphosphorus pentoxide.

5. Writing a reaction • You must include formulas for all substances. • You may include states [(s), (l), (g), (aq)] • You should balance the reaction Do not include masses—even if they are part of the problem, they are not part of the reaction

6. Write the reaction • Aqueous sodium bromide and chlorine gas form aqueous sodium chloride and liquid bromine • Silver (I) oxide decomposes to form solid silver and oxygen gas • Solid phosphorus burns in oxygen gas to for diphosphorus pentoxide. NaBr (aq) + Cl2 (g) NaCl (aq) + Br2(l) Ag2O(s)  Ag (s) + O2(g) P4 (s) + O2 (g) P2O5 (s)

7. But… NaBr (aq) + Cl2 (g) NaCl (aq) + Br2(l) + +

8. But… NaBr (aq) + Cl2 (g) NaCl (aq) + Br2(l) + + Seems to contradict Dalton’s Atomic Theory

9. But… 2NaBr(aq) +Cl2 (g)2NaCl(aq) + Br2(l) + + That’s better. It’s balanced!

10. But… 2NaBr(aq) +Cl2 (g)2NaCl(aq) + Br2(l) These are coefficients

11. But… 2NaBr(aq) +Cl2 (g)2NaCl(aq) + Br2(l) Coefficients indicate moles or particles of the substance

12. But… 2NaBr(aq) +Cl2 (g)2NaCl(aq) + Br2(l) No coefficient? It means there is a 1 (not written in)

13. Count your atoms: • H20 • As2O3 • Ca(NO3)2 • 3 Al2(SO4)3 • 2 NH4NO3

14. The T diagram • Na Na • Br Br • Cl Cl NaBr(aq) +Cl2 (g)NaCl(aq) + Br2(l)

15. Never change a good formula! • Count all atoms in reactants and products • Fix a count by changing a coefficient • Repeat steps 1-2 as needed

16. The T diagram • Na 1 Na 1 • Br 1 Br 2 • Cl 2 Cl 1 NaBr(aq) +Cl2 (g)NaCl(aq) + Br2(l)

17. You need to double the bromine on the left.

18. You need to double the bromine on the left. • Do not try this at home or anywhere! NaBr2 Na2Br NaBr2 • Sodium bromide is NaBr

19. You need to double the bromine on the left. • Do not try this at home or anywhere! NaBr2 Na2Br NaBr2 • Sodium bromide is NaBr • Two Sodium bromide is 2 NaBr

20. The T diagram • Na 1 2 Na 1 • Br 1 2 Br 2 • Cl 2 Cl 1 2NaBr(aq) +Cl2 (g)NaCl(aq) + Br2(l) Recount

21. The T diagram • Na 1 2 Na 1 2 • Br 1 2 Br 2 • Cl 2 Cl 1 2 2NaBr(aq) +Cl2 (g)2NaCl(aq) + Br2(l) Recount

22. Easy • __N2 + __O2 __ NO • __N2 + __ H2__ NH3 • __S8 + __ F2  __ SF4 • __ NaI + __Br2 __I2 + __ NaBr

23. If it gets tough: • Start with elements that only show up twice. • If one side is even, and the other is odd—double the odd one. • Leave hydrogen, oxygen and any pure elements to the very end.

24. Medium • __NH3+_NaOCl_N2H4+_NaCl+_H2O • __Ca2C +__ H2O __CH4+__ Ca(OH)2 • __ NH3 + __ O2__ NO + __ H2O • ___C4H10O + ___O2___CO2+___H2O

25. “Am I being punished?” • (Later)

26. Types of reactions

27. Synthesis or composition A+BAB Only 1 product!

28. Decomposition AB  A+B Only 1 reactant!

29. Single replacement A+BC  AC+B or D+BC  BD+C A pure element in reactants and products!

30. Double replacement AB+CD  AD+CB Two ionic compounds switch partners!

31. Combustion (burning or oxidation) AB+O2 AOx+BOy Oxygen is a reactant!

32. Other Oxidation/Reduction AB+CD  a whole bunch of other things.

33. Double replacement AB+CD  AD+BC If both AD and BC are ionic compounds that dissolve in water—the product never comes together

34. Two types of double replacement AB+CD  AD+BC In a neutralization reaction, A=H+, D=OH-, so AD=water

35. Write and balance: • HCl +NaOH • H2SO4 + KOH • H3PO4 + Al(OH)3 • HClO4 + Ba(OH)2  A neutralization reaction forms a salt and water

36. Write and balance: • HCl +NaOH H2O +NaCl • H2SO4 + KOH K2SO4 + H2O • H3PO4 + Al(OH)3 AlPO4 + 3H2O • 2HClO4 + Ba(OH)2  2H2O+ Ba(ClO4)2 A neutralization reaction forms a salt and water

37. Two types of double replacement AB+CD  AD+BC In a precipitation reaction, one of the products won’t dissolve.

38. For example: NaCl(aq)+AgNO3(aq) NaNO3(aq)+AgCl(s) NaNO3 dissolves in water, AgCl doesn’t AgCl is the precipitate

39. No precipitate=no reaction NaNO3(aq)+KCl(aq) All of these dissolve in water Before Contents: aqueous Na+ Cl- K+ NO3-

40. No precipitate=no reaction KNO3(aq)+NaCl(aq) All of these dissolve in water Before After Contents: aqueous Na+ Cl- K+ NO3-

41. Better yet: NaCl(aq)+AgNO3(aq) NaNO3(aq)+AgCl(s) Ag+(aq) + Cl-(aq) AgCl(s) The sodium and nitrate ions (not changed in the reaction) are spectator ions, omit them

42. Do you want to save some trouble? NaCl(aq)+AgNO3(aq) NaNO3(aq)+AgCl(s) is Ag+(aq) + Cl-(aq) AgCl(s) This is the net ionic equation

43. Review Questions: • Your lab. • It’s not a question.

44. Mole conversions review: • How many moles of Mg are in 36.0 g Mg? • What is the formula mass of Mg3N2? • What is the mass of .49 moles Mg3N2 • Write and balance: Magnesium metal and nitrogen gas form solid magnesium nitride • In this reaction: how many moles of magnesium nitride can be made from 1.48 mol of magnesium?

45. The mass to mass problem g 1 mol mol g 1 mol g mol g

46. The mass to mass problem g 1 mol mol g 1 mol g mol Given Value g

47. The mass to mass problem g 1 mol mol g 1 mol g mol Formula Mass g

48. The mass to mass problem g 1 mol mol g 1 mol g mol Mole ratio (from a balanced reaction) g

49. The mass to mass problem g 1 mol mol g 1 mol g mol Formula Mass g

50. The mass to mass problem g 1 mol mol g 1 mol g mol Answer (probably wrong) g