ELECTOCHEMISTRY Oxidation-Reduction: -Oxidation is loss of electrons -Reduction is gain of electrons -Oxidizing agent species that does oxidation taking electron from the substance -Reducing agent species that does reduction giving electron to the substance -Substance after oxidation by losing electron becomes positively charged or has more positive or less negative and hence has higher oxidation number. -Reduction is the process where substance gain electron making it more negative and lower the positive •Electron loss always has electron gain •The oxidizing agent is reduced and reducing agent is oxidized •The total number of electron gained by the atoms/ions of that oxidizing agent alwaysequal to the number lost by the atoms/ions of the reducing agent So gain of oxidizing agent = loss of reducing agentBalancing Redox reactions: There are two methods to balance redox reactions. -Oxidation number method, and -Half-reaction method. -Half-reaction methodis based on oxidation and reduction reactions separately -It divides the overall redox reaction into oxidation and reduction half-reaction -Each half-reaction is balanced for atoms and charge -One or both are multiplied by some integer to make electron gain equal to lost -The half-reactions are combined -Electro chemistry depends on Redox reactions -Electricity is motion of electron and Redox reactions are reactions of transfer of electrons -The half-reaction method is essential in study of electrochemistry -It separates the oxidation and reduction steps – This reflects their actual physical separation in electrochemical cells -It is easy to balance Redox reactions that take place in acidic or basic solution which is common in electrochemical cells . -It usually does not require assigning O N s -We start up with a skeleton ionic reaction -We have species that are oxidized and reduced -The oxidized form of a species is on the left side and reduced form of species is on the Right side of the equation
We carry out balancing in the following steps: Step 1: Divide the skeleton reaction into two half reaction, each of which contains the oxidized and reduced forms of one of the species. Step 2: Balance the atoms and charges in each half-reaction -Atoms are balanced in order: Atoms other than O and H, then O, and then H. -Charge is balanced by adding electrons (e− ) They are added to the left in the reduction half-reaction the reactants gain them; they are added to the right in the oxidation half-reaction because the reactant loses them. Step 3: If necessary multiply one or both half reactions by an integer to make the number of (e− ) gained in the reduction equals the number lost in the oxidation. Step 4: Add the balanced half-reaction, and include states of matter.