CHAPTER 3-A Moles, Masses, and Chemical Equations

1. CHAPTER 3-A Moles, Masses, and Chemical Equations © 2012 by W. W. Norton & Company

2. The Structure of Atoms Atomic Mass Unit 1 amu = 1/12 of the mass of on atom of Carbon-12 1 amu = 1.6605 x 10-24 g

3. Atomic and Molecular Mass Mass: proton = 1.00728 amu neutron = 1.0086 amu electron = 0.0005486 12C atom = 12.00000 amu 13C atom = 13.00335 amu

4. Atomic and Molecular Mass • The atomic masses as tabulated in the periodic table are the averages of the naturally occurring isotopes. • Mass of C = average of 12C and 13C • = 0.9889 x 12 amu + 0.0111 x 13.0034 amu • = 12.011 amu

5. Atomic and Molecular Mass The mass of a molecule is just the sum of the masses of the atoms making up the molecule. m(C2H4O2) = 2·mC + 4·mH + 2·mO • = 2·(12.01) + 4·(1.01) + 2·(16.00) • = 60.06 amu

6. Avogadro and the Mole • One mole of a substance is the gram mass value equal to the amu mass of the substance. • One mole of any substance contains 6.02 x 1023 units of that substance. • Avogadro’s Number (NA,6.022 x 1023) is the numerical value assigned to the unit, 1 mole.

7. Avogadro and the Mole

8. Methionine, an amino acid used by organisms to make proteins, is represented below. Write the formula for methionine and calculate its molar mass. (red = O; gray = C; blue = N; yellow = S; ivory = H) Avogadro and the Mole

9. The Mole: Allows us to make comparisons between substances that have different masses. Avogadro and the Mole

10. Balancing Chemical Equations • A balanced chemical equation represents the conversion of the reactants to products such that the number of atoms of each element is conserved. reactants  products limestone  quicklime + gas Calcium carbonate  calcium oxide + carbon dioxide CaCO3(s)  CaO(s) + CO2(g)

11. Balancing Chemical Equations CaCO3(s)  CaO(s) + CO2(g) The letters in parentheses following each substance are called State Symbols (g) → gas (l) → liquid (s) → solid (aq) → aqueous

12. Balancing Chemical Equations A balanced equation MUST have the same number of atoms of each element on both sides of the equation. H2 + O2→ H2O Not Balanced H2 + ½O2→ H2O Balanced 2H2 + O2→ 2H2O Balanced

13. Balancing Chemical Equations The numbers multiplying chemical formulas in a chemical equation are called: Stoichiometric Coefficients (S.C.) 2H2 + O2→ 2H2O Balanced Here 2, 1, and 2 are stoichiometric coefficients.

14. Balancing Chemical Equations Hints for Balancing Chemical Equations: • Save single element molecules for last. • Try not to change the S.C. of a molecule containing an element that is already balanced. • If possible, begin with the most complex molecule that has no elements balanced.

15. Balancing Chemical Equations Hints for Balancing Chemical Equations: 4) Otherwise, trial and error!!

16. Balancing Chemical Equations Example 1: CH4 + O2→ CO2 + H2O Balance O2 last C is already balanced Start by changing S.C. of H2O to balance H CH4 + O2→ CO2 + 2H2O

17. Balancing Chemical Equations Example 1: CH4 + O2→ CO2 + 2H2O Now C and H are balanced Balance O by changing the S.C. of O2 CH4 + 2O2→ CO2 + 2H2O BALANCED!

18. Balancing Chemical Equations Example 2: B2H6 + O2→ B2O3 + H2O Balance O last B is already balanced Start by changing S.C. of H2O: B2H6 + O2→ B2O3 + 3H2O

19. Balancing Chemical Equations Example 2: B2H6 + O2→ B2O3 + 3H2O B and H are balanced Balance O by changing S.C. of O2 B2H6 + 3O2→ B2O3 + 3H2O BALANCED!

20. Balancing Chemical Equations Example 3: MnO2 + KOH + O2→ K2MnO4 + H2O Balance O last Mn is already balanced Change S.C. of KOH to balance K MnO2 + 2KOH + O2→ K2MnO4 + H2O

21. Balancing Chemical Equations Example 3: MnO2 + 2KOH + O2→ K2MnO4 + H2O Mn, K, and H are balanced (H was balanced by chance) Balance O MnO2 + 2KOH + ½O2→ K2MnO4 + H2O or 2MnO2 + 4KOH + O2→ 2K2MnO4 + 2H2O

22. Balancing Chemical Equations Example 4: NaNO2 + H2SO4→ NO + HNO3 + H2O + Na2SO4 Hard one (no single element molecules) S is balanced Start with NaNO2 to balance Na 2NaNO2 + H2SO4→ NO + HNO3 + H2O + Na2SO4

23. Balancing Chemical Equations Example 4: 2NaNO2 + H2SO4→ NO + HNO3 + H2O + Na2SO4 S, Na, and N are balanced Cannot balance H without changing S.C. for H2SO4! Boo! Option 1: trial and error Option 2: Go on to next problem!

24. Balance the following equations: C6H12O6→ C2H6O + CO2 Fe + O2→ Fe2O3 NH3 + Cl2→ N2H4 + NH4Cl KClO3 + C12H22O11→ KCl + CO2 + H2O Balancing Chemical Equations

26. Balance the following equations: C6H12O6→ 2C2H6O + 2CO2 Fe + O2→ Fe2O3 NH3 + Cl2→ N2H4 + NH4Cl KClO3 + C12H22O11→ KCl + CO2 + H2O Balancing Chemical Equations

27. Balance the following equations: C6H12O6→ 2C2H6O + 2CO2 4Fe + 3O2→ 2Fe2O3 (balance O first) NH3 + Cl2→ N2H4 + NH4Cl KClO3 + C12H22O11→ KCl + CO2 + H2O Balancing Chemical Equations

28. Balance the following equations: C6H12O6→ 2C2H6O + 2CO2 4Fe + 3O2→ 2Fe2O3 (balance O first) NH3 + Cl2→ N2H4 + NH4Cl N:H is 1:3 on left, must get 1:3 on right! Balancing Chemical Equations

29. NH3 + Cl2→ N2H4 + NH4Cl N:H is 1:3 on left, must get 1:3 on right! 4NH3 + Cl2→ N2H4 + 2NH4Cl Balancing Chemical Equations

30. Balance the following equations: C6H12O6→ 2C2H6O + 2CO2 4Fe + 3O2→ 2Fe2O3 4NH3 + Cl2→ N2H4 + 2NH4Cl KClO3 + C12H22O11→ KCl + CO2 + H2O (tough!) Balancing Chemical Equations

31. Balance the following equations: KClO3 + C12H22O11→ KCl + CO2 + H2O balance C KClO3 + C12H22O11→ KCl + 12CO2 + H2O balance H KClO3 + C12H22O11→ KCl + 12CO2 + 11H2O balance O 8KClO3 + C12H22O11→ KCl + 12CO2 + 11H2O Balancing Chemical Equations

32. Balance the following equations: 8KClO3 + C12H22O11→ KCl + 12CO2 + 11H2O balance K (and hope Cl is balanced) 8KClO3 + C12H22O11→ 8KCl + 12CO2 + 11H2O Balanced! Balancing Chemical Equations

33. Write a balanced equation for the reaction of element A (red spheres) with element B (green spheres) as represented below: Balancing Chemical Equations