Mno 2 oxidation reduction step 2balance each half

–
MnO
2
Oxidation:
Reduction:
Step 2: Balance each half reaction with regard to atoms other than O
and H.
Oxidation:
Reduction:
CN
–
CNO
–
MnO
4
–
MnO
2

Balancing Redox Reactions
Step 3: Balance O by adding H
2
O.
Oxidation:
Reduction:
Step 4: Balance H by adding H
+
.
Oxidation:
Reduction:
H
2
O + CN
–
CNO
–
MnO
4
–
MnO
2
+ 2H
2
O
H
2
O + CN
–
CNO
–
+ 2H
+
4H
+
+ MnO
4
–
MnO
2
+ 2H
2
O
Balance the following reaction in basic solution:
CN
–
+ MnO
4
–
CNO
–
+ MnO
2

Balancing Redox Reactions
Step 5: Balance charge by adding electrons.
Oxidation:
Reduction:
–1 –1
0 0
Total charge:
Total charge:
H
2
O + CN
–
CNO
–
+ 2H
+
+ 2e
–
3e
–
+ 4H
+
+ MnO
4
–
MnO
2
+ 2H
2
O
Balance the following reaction in basic solution:
CN
–
+ MnO
4
–
CNO
–
+ MnO
2

Balancing Redox Reactions
Step 6: If the number of electrons in the half reactions are not
equal, multiply as necessary to make them equal.
Oxidation:
Reduction:
3( )
Balance the following reaction in basic solution:
CN
–
+ MnO
4
–
CNO
–
+ MnO
2
H
2
O + CN
–
CNO
–
+ 2H
+
+ 2e
–
3e
–
+ 4H
+
+ MnO
4
–
MnO
2
+ 2H
2
O 2( )
3H
2
O + 3CN – 3CNO – + 6H + + 6e –
6e
–
+ 8H
+
+ 2MnO
4
–
2MnO
2
+ 4H
2
O

6e
–
+ 8H
+
+ 2MnO
4
–
2MnO
2
+ 4H
2
O
3H
2
O + 3CN
–
3CNO
–
+ 6H
+
+ 6e
–
Balancing Redox Reactions
Step 7: Add the half-reactions together and cancel electrons
Oxidation:
Reduction:
3CN – + 2H + + 2MnO
4
– 3CNO – + 2MnO
2
+ H
2
O
Balance the following reaction in basic solution:
CN
–
+ MnO
4
–
CNO
–
+ MnO
2

Balancing Redox Reactions
Step 8: Add one OH
–
for every H
+
to both sides of the equation.
3CN – + 2H + + 2MnO
4
– 3CNO – + 2MnO
2
+ H
2
O
Balance the following reaction in basic solution:
CN
–
+ MnO
4
–
CNO
–
+ MnO
2
+ 2OH – + 2OH –
3CN
–
+ 2H
2
O + 2MnO
4
–
3CNO
–
+ 2MnO
2
+ H
2
O + 2OH
–
Step 9: Cancel water molecules as necessary.
3CN – + H
2
O + 2MnO
4
– 3CNO – + 2MnO
2
+ 2OH –

Balancing Redox Reactions
• Write 2 half-reactions
Identify the species oxidized and reduced
• Balance the atoms others than O and H using the appropriate stoichiometric coefficients
Balance O atoms adding H
2
O
Balance H atoms adding H
+
Balance masses
• Add electrons to the side with excess positive charge
Balance charges
• Multiply each half-reaction by a coefficient so that the number of electrons gained and
lost are the same
Balance electrons
• Cancel terms that appear on both sides of the overall equation
• IF SOLUTION IS ALKALINE: Add OH - on both sides and cancel out water as
necessary.
Combine the half-reactions

Electrochemical Cells
• A galvanic cell uses a spontaneous redox reaction
(Δ G < 0) to generate electrical energy.
• The system does work on the surroundings.
• A electrolytic cell uses electrical energy to drive a
nonspontaneous reaction (Δ G > 0).
• The surroundings do work on the system.

Electrochemical Cells