Outline for Today Friday, Oct. 5 Review of Balancing - - PowerPoint PPT Presentation

Outline for Today

Friday, Oct. 5

• Review of Balancing Reduction-Oxidation Reactions
• Chapter 5: Thermochemistry
• How is energy transferred or transformed in chemical

reactions?

• How can we qualitatively keep track of energy in a

chemical reaction?

• Where does our energy come from?

Balancing Redox Half Reactions (Section 20.2)

• Example 1. Balance:

Cu(s)+NO3- → Cu2+ (aq) +NO2 (g)

• Example 2. Balance:

MnO4- (aq) + C2O42- (aq) → Mn2+ (aq) + CO2 (g)

Balancing Redox Reactions

• 1. Separate total reaction into two half reactions.
• 2. Assign Oxidation Numbers to each atom
• 3. Balance each half reaction:
• A. Balance all elements besides H and O
• B. Balance O by adding H2O
• C. Balance H by adding H+
• D. Balance charge by adding e-

4. Multiply half reactions by integers so that half reactions have equal number of electrons 5. Add the half reactions and simplify!

Determining Oxidation Numbers

Species

Oxidation Number

Elemental Atoms Monoatomic Ion

Charge on Ion

Hydrogen Bonded to Nonmetal

“+1

Hydrogen Bonded to Metal

• 1

Oxygen

Usually -2

Fluorine

• 1

Other Halogens

Usually -1

Neutral Molecule

Sum of Oxidation Numbers is 0

Polyatomic Ion

Sum of Oxidation Numbers is Ion charge

O2 (g) + 4H+ (aq) + 4e-→ 2H2O (l)

Reduction-Oxidation Reactions are the Reactions that Sustain Life

C6H12O6 + 6 O2 → 6 CO2 + 6 H2O 6 CO2 + 6 H2O → C6H12O6 + 6 O2

We Burn Fuels: Plants Make Fuels from Solar Energy:

+1

• 2

+4 -2

Oxidation Numbers: