How do I balance oxidation-reduction equations?

[gigi9]

Someone please give me a good explanation on how to "Balance Oxidation- Reduction Equations." Plz show me the steps and an example of how to do this type of equations. Thanks a lot.

 

[arcnets]

gigi9,
photosynthesis might be a good example. Let's start from
H₂O + CO₂ -> C₆H₁₂O₆ + O₂.
First step, let's add what we have.
Left-hand side: 2H + 3O + 1C.
Right-hand side: 12H + 8O + 6C. So the formula is not balanced.

As a first step, we should look for an element that appears only in one component on each side. This is carbon. So, to balance carbon, we have to use 6 molecules of carbon dioxide:
H₂O + 6CO₂ -> C₆H₁₂O₆ + O₂.
Let's add what we have.
Left-hand side: 2H + 13O + 6C.
Right-hand side: 12H + 8O + 6C.

Is there another element which appears only once on each side? Yes, hydrogen! So we better use 6 molecules of water:
6H₂O + 6CO₂ -> C₆H₁₂O₆ + O₂.
Left-hand side: 12H + 18O + 6C.
Right-hand side: 12H + 8O + 6C.

We can balance this by adding more oxygen on the RHS:
6H₂O + 6CO₂ -> C₆H₁₂O₆ + 6O₂.

Now it's balanced.

 

[Chemicalsuperfreak]

Originally posted by arcnets
gigi9,
photosynthesis might be a good example. Let's start from
H₂O + CO₂ -> C₆H₁₂O₆ + O₂.
First step, let's add what we have.
Left-hand side: 2H + 3O + 1C.
Right-hand side: 12H + 8O + 6C. So the formula is not balanced.

As a first step, we should look for an element that appears only in one component on each side. This is carbon. So, to balance carbon, we have to use 6 molecules of carbon dioxide:
H₂O + 6CO₂ -> C₆H₁₂O₆ + O₂.
Let's add what we have.
Left-hand side: 2H + 13O + 6C.
Right-hand side: 12H + 8O + 6C.

Is there another element which appears only once on each side? Yes, hydrogen! So we better use 6 molecules of water:
6H₂O + 6CO₂ -> C₆H₁₂O₆ + O₂.
Left-hand side: 12H + 18O + 6C.
Right-hand side: 12H + 8O + 6C.

We can balance this by adding more oxygen on the RHS:
6H₂O + 6CO₂ -> C₆H₁₂O₆ + 6O₂.

Now it's balanced.

That's good arcnets, but gigi is talking about balancing redox reactions, which is a bit more complicated than regular stoichiometry.

 

[HazZy]

why don't you post an example and we'll work from there gigi9.