For example let's take Iron, which can have the valency of 2 and 3, the question is, what factors affect the valency changes of iron, like, how to change the valency of Iron from 3 to 2?

Both iron compounds in oxidation state of +2 or +3 are stable. Depending on its chemcial and physical environment they would interchange in some cases. Like a iron (II) compound like FeSO4 if left in air it would be converted to iron (III). If you want to know if an equation you have written is feasible in energetical terms, just check up the reduction potential table. If you want to make iron from its +3 state back to +2 state it has to be the cathode and undergoes reduction.

 

But probably this question should not belong to 'organic chemistry' session...

Right, thank you

I am transferring my question from organic chemistry section to this one. For example let's take Iron, which can have the valency of 2 and 3, the question is, what factors affect the valency changes of iron, like, how to change the valency of Iron from 3 to 2?

Merged and moved. No need to start a new thread. If you need a thread to be moved, please ask rather than starting a duplicate.

Where is the topic moved to? I can't find it

Factors which affect the change in valency include.

1) Successive ionisation energies

2) Lattice energies

3) strength of covalent ligand to metal bonds

4) whether ligands pi donate, or pi accept

5) crystal field stabilisation energy particularly low spin/high spin changes

6) solvation energies

7) etc etc etc