Consider the half reactions below for a chemical reaction.
> zn²⁺(aq)+2e⁻
cu²⁺(aq)+2e⁻> cu(s)
what is the overall equation for this chemical reaction?

Explanation:

Redox couple  

It is defined as : having together the oxidized and reduced forms of a substance taking part in oxidation or reduction half reactions .they are actually conjugate acid base pairs

.we can also define it as : an oxidizing and reducing agent which appear on opposite sides of a half equation constitute the redox couple .Like, given below is the cell in which we consider Zn/Cu redox couple .

Electrochemical cell

•Electrochemical cell is the cell in which chemical energy gets converted to electric energy.  

•In it indirect redox reactions takes place.  

•These reactions are spontaneous that is free energy change for this reaction is negative.

•This cell consists of two half cells.  

•In one half cell , there is a aqueous 1molar Zinc sulphate solution with Zinc rod dipped in it.

•In other half cell, there is a 1 molar aqueous solution of Copper sulphate solution with Copper rod dipped in it.

•These electrodes by means of wire are attached to galvanometer.

•  A U-shaped tube is taken, which is sealed from both the ends with cotton plug.

•In this, the electrolyte that is inert electrolyte is taken like Potassium nitrate, Ammonium nitrate etc. The electrolyte present is in semi-liquid state.

Observations

With time we see that Zinc rod loses weight, as it has more tendency to loose electrons that is:

These electrons released by zinc, travel to another beaker by means of wire. In doing so, they cause deflection in galvanometer and produce current. This current travel in the direction opposite to the flow of electrons.

These electrons move to another half cell, where copper ions gain these electrons that is reduction occur. As a result, copper metal start depositing on electrode.

The overall reaction that occurs is shown below:

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