Answers to Katy

Hi Katy, concerning the reaction between nitrogen and hydrogen gas to produce ammonia
N2 + H2 → NH3
The oxidation number of N decreases from zero to -3, this is reduction.
(N + 3e → N-3) × 2 so 2N + 6e→ 2N-3
(H → H+ + 1e) × 6 so 6H → 6H+ + 6e
2N + 6H → 2N-3 + 6H+
so the balanced equation:
N2 + 3H2 → 2NH3

The other question: The cell in which electroplating occurs is called an electrolytic cell. Eectroplating is a form of electrolysis.Whenever you are passing an electric current to start a chemical reaction, electrolysis is involved.

Third question: Electrolysis of water in the presence of KNO3
Cathode 1/2 reaction:
2H2O + 2e → H2 + 2OH-
in this 1/2 reaction, the O.N. of H decreases from +1 to 0. this is reduction. But only 2 hydrogens of the 4 hydrogens in the reactants were reduced. The other 2 hydrogens were neither oxidized nor reduced. In the compound OH-, the oxidation number of H is +1, which indicates that the O.N. of the 2 hydrogens in 2OH- did not change from that of reactant.
Reduction 1/2 reaction:
2H2O → O2 + 4H+ + 4e
in this 1/2 reaction, the O.N. of oxygen increased from -2 to 0, so this is oxidation. On the other hand, the oxidation number of hydrogen in the reactants and products is the same: +1
As for the question about the galvanic cell,
In the anode half cell, the amount of cations in the solution are increasing (remember that the atoms of the metal are being oxidized to cations) , so the amount of positive charges increases, therefore, anions flow from the salt bridge to maintain electric neutrality at this half cell.
conversely, cations flow from the salt bridge to the cathode half cell solution, because the solution is losing cations (cations are reduced to atoms), and the amount of anions in solution (sulfate ions for exampe if the solution is zinc sulfate) is becoming much more than the cation.
If you're question is: why do ions flow from salt bridge to maintain electric neutrality? What makes them flow in the first place?
Well, this would be an advanced question...flow of ions is controlled by a special diffusion called Fickian diffusion...If you like to read about it, you can..but it's not required from you this year