Lead Accumulator

Lead Accumulator

The lead accumulator refers to a secondary cell as the electrical energy doesn't generate itself inside the cell, but it is stored prior to an external source. It's a reversible cell as the cell reactions are in the reversed state if external emf is more than the emf of the cell. Therefore, in this cell, total cell reaction are reversed by exerting external opposite to e.m.f which is greater than e.m.f of the cell. A good secondary cell can undergo a large number of discharging and charging cycles.
This cell has the capability to store the electrical energy from charging or from the external source, and can supply process is done at the time of discharge. Energy is stored in chemical energy form. So, this cell refers to an accumulator or the storage cell or the storage battery. Voltage of the cell is depend on the strength of the solution of sulphuric acid used as electrolyte but not dependent on electrodes' size or its cell's size.

A lead accumulator consists of lead plates as the negative electrode. Lead plates impregnated with lead oxide act as the positive electrode. Negative and positive electrodes are arranged in an alternate manner. This assembly of lead plates is dipped in a non-conducting vessel made up of glass or plastic or ebonite and containing 38% sulphuric acid. All positive plates are connected to each other and all negative plates are connected to each other.

When the cell starts to work, oxidation occurs on the lead plates and the reduction occurs in the lead plates with PbO i.e. Lead Oxide. This is known as the discharging of the cell.

The cell reactions when the battery is in use are given below-
Anode: Pb(s) + SO₄⁻²(aq) → PbSO₄(s) + 2e
Cathode: PbO₂(s) + SO₄⁻²(aq) + 4H⁺(aq) + 2e– → PbSO₄(s) + 2H₂O (l)
Overall cell reaction consisting of cathode and anode reactions is-
Pb(s) + PbO₂(s) + 2H₂SO₄(aq) → 2PbSO₄(s) + 2H₂O(l)
On charging the battery the reaction is reversed and PbSO₄(s) on anode and cathode is converted into Pb and PbO₂, respectively.

When external emf which is greater than the emf of the cell is applied into the cell, then there are accurate reverse reactions taking place. The Oxidation occurs on positive electrodes and reduction at negative electrodes. This is referred to as the charging of the cell.
Reaction at negative electrode (Cathode)-
PbSO_4(s) + 2e^– → Pb_(s) + SO₄^–2
Reaction at positive electrode (Anode)-
PbSO₄(s) + 2H₂O(l) → PbO₂(s) + 4H⁺ + SO₄^–2 + 2e^–
Net cell reaction during charging-
Pb_(s) + PbO_2(s) + 2H₂SO_4(aq) → 2 PbSO_4(s) + 2H₂O_(l)

Uses of Lead Accumulator

1. Lead accumulators are used in motor cars and in different automobiles vehicles as a consequence, they are well-known as car batteries.
2. Lead accumulators are used in telegraph offices and telephone.
3. They have the use of radio sets, electric clocks, burglar's alarms, etc.
4. Used in scientific laboratories as the constant DC voltage source.

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