Oxidation - involves the loss of electrons or hydrogen OR gain of
oxygen OR increase in oxidation state
Reduction - involves the gain of electrons or hydrogen OR loss of oxygen
OR decrease in oxidation state 
1.H2 + F2 ? 2 HF


The overall reaction may be written
as two half-reactions:


H2 ? 2 H+ + 2
e- (the oxidation reaction)


F2 + 2 e- ? 2
F- (the reduction reaction)


There is no net change in charge in
a redox reaction so the excess electrons in the oxidation reaction must equal
the number of electrons consumed by the reduction reaction. The ions combine to
form hydrogen fluoride:


H2 + F2 ? 2 H+
+ 2 F- ? 2 HF 


2. 2AgCl(s) + H2(g) ? 2 H+(aq)
+ 2 Ag(s) + 2 Cl


AgCl


Ag has a +1 oxidation state 


Cl has a -1 oxidation state 


H2 has an oxidation state
of zero
H+ has a +1 oxidation state


Ag has an oxidation state of zero.
Cl- has a -1 oxidation state.
Ag went from +1 in AgCl to 0 in Ag. The silver
     atom gained an electron.H went from 0 in H2 to +1 in H+.
     The hydrogen atom lost an electron.Cl kept its oxidation state constant at -1 throughout
     the reaction.Silver gained an electron. This means the silver was
     reduced.Hydrogen lost an electron. This means the hydrogen gas
     was oxidized.Its oxidation state was increased by one.. Chlorine's
     oxidation state was unchanged throughout the reaction.


3.2Na + Cl2 ------->2NaCl


Na –loss of 2 e-


Cl –gain of 2e-


4.2Na + O2-------->Na2O


Na-loss of 2 e-
O -gain 2 e-
5.2Na + S ------->Na2S


Na-loss of 2e-


S-gain of 2 e- 
Thanks & Regard
Aarti Gupta
askiitians Faculty





						

							
Zn(s) + CuSO4(aq) ? ZnSO4(aq) + Cu(s)
Copperbegins in the +2 oxidation state and is reduced to a neutral state over the course of the reaction. Zinc begins neutral and is oxidized to the +2 state.
The oxidation half-reaction is:
Zn(s) ? Zn2++ 2e-
The reduction half-reaction is:
Cu2++ 2e-? Cu(s)
Sample 1. equation: 2 H2+ O2? 2 H2O
The sum of oxidation states in the reactants is equal to that in the products: 0 + 0 ? (2)(+1) + (-2)
In this equation both H2and O2are free elements and their oxidation states are 0. Theproductis H2O, in which the oxidation state of oxygen is -2 and that of each hydrogen is +1.
Sample 2. equation: 2 H2O ? 2 H2+ O2
Calculation: (2)(+1) + (-2) = 0 ? 0 + 0
In this equation the water is "decomposed" into hydrogen and oxygen, which are both neutral. Similar to the previous example, the H2O has a total oxidation state of 0, with each H taking on a +1 state and the O being -2. Thus, decomposition oxidizes oxygen from -2 to 0 and reduces hydrogen from +1 to 0.
Sample 3. equation: Cl2+ 2 NaBr ? 2 NaCl + Br2
Calculation: (0) + ((+1) + (-1) = 0) -> ((+1) + (-1) = (0) + 0
In this equation Br is replaced with Cl and Cl is reduced, while Br is oxidized.Sample 4. equation: Fe2O3+ 6 HCl ? 2 FeCl3+ 3 H2O
Explanation: In this equation Fe and H trade places and O and Cl trade places.

Reaction: 2H2O2(aq) ? 2H2O(l) + O2(g)
In the reactants H has an O has an O.S. of -1, which changes to -2 for the product, H2O (reduced) and 0 for the product, O2 (oxidized).
Thanks & Regards
Rinkoo Gupta
AskIITians Faculty