Chemical Cells

When we place two metals of different reactivity in an electrolyte, we can create a simple cell that produces electricity. Electrons will flow from the more reactive metal to the less reactive metal. We can use this flow of electrons to power an electrical circuit.

An electrolysis apparatus with the left electrode labelled "less reactive metal" and the electrode on the right labelled "more reactive metal".

  • An electrolyte is a substance that conducts electricity when in a molten state or in solution.

For example, we can place a strip of copper and a strip of zinc in an electrolyte solution and connect them to a voltmeter to measure the voltage between them.

An electrolysis apparatus with the left positive electrode labelled as "copper" and the right negative electrode labelled "zinc".

  • This is a simple cell made with copper (Cu) and zinc (Zn)

Zinc is more reactive than copper, which means it loses electrons more easily. The zinc atoms lose electrons to form positive ions, which go into the aqueous solution and decrease the mass of the zinc electrode.

Zn(s)Zn²⁺ (aq) + 2e⁻

These electrons flow around the circuit, from the zinc electrode to the less reactive electrode (copper). The two electrons from the zinc atom convert a copper ion from solution into a copper atom, which deposits on the copper electrode, increasing its mass.

Cu²⁺ + 2e⁻ → Cu(s)

This sets up a charge difference between the two electrodes. The greater the difference in reactivity between the two metals, the greater the voltage.

The chemicals in the cell eventually run out, so the reactions eventually stop. This means that the cell can only produce electricity for a limited period of time.

To determine which metals we can use for an electrical cell, we can use the reactivity series. This series shows the most reactive metals at the top and the least reactive metals at the bottom.

The reactivity series including magnesium, aluminium, zinc, iron, tin, lead, and copper , each with their atomic symbols. An arrow pointing upwards indicates that reactivity increases as you move up the series.

Batteries

We can create a battery by connecting two or more cells in series. This produces a greater voltage than a single cell. There are two types of batteries:

  • Rechargeable batteries
  • Non-rechargeable batteries

The reactants in non-rechargeable batteries, such as alkaline batteries, are eventually depleted. Once these reactants are depleted, the battery will stop producing electricity.

On the other hand, rechargeable batteries can be charged by applying an electrical current. This reverses the chemical reactions, allowing the battery to be recharged and used again.

Both types of batteries have their advantages and disadvantages. Non-rechargeable batteries tend to be cheaper and more convenient for single-use applications. However, rechargeable batteries are more cost-effective in the long run and better for the environment, since they can be reused multiple times.

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