Cells and Batteries

• What cells do

  • Placing 2  different metals into an electrolyte can produce electricity 
  • This is what happens in a simple cell - cells are used to generate electricity (The chemicals in the cell react together to release electricity) 
  • Remember that an electrolyte is a solution that conducts electricity (e.g. a solution of an ionic compound)

  
• Explain how the cell below produces electricity

  • The strip of copper and strip of magnesium are being used as electrodes and have been placed into the electrolyte 
  • Connecting the 2 metals to the voltmeter creates a potential difference / voltage between them , - in other words, a chemical reaction is taking place on the surface of the 2 metals 
  • And because of this, an electric current will flow through the wire  

  
• Limitations of a simple cell

  • The diagram of the cell below is a very simplified version of an electrical cell 
  • A cell such as this one would not generate an electrical current for very long 
  • The cells that we use in chemistry are slightly more complicated

  
• Why cells only produce electricity for a certain period of time

  • A cell can only produce electricity for a certain period of time 
  • Eventually the chemicals in the cell run out and the reaction stops
• How Reactivity affects Potential difference?

  • Cells only produce electricity if we use metals with different reactivities 
  • We can use the Reactivity Series to choose the metals for the electrical cell 
  • The size of the potential difference produced depends on the difference in the reactivity between the two metals 
  • A cell containing magnesium and copper will have a large potential difference  
  • A cell containing zinc and tin will have a small potential difference 
  • The greater the difference between the reactivity of the metals, the greater the potential difference produced by the cell

  
• As well as the reactivity of the 2 metals used in the cell, the electrolyte in the cell also affects reactivity
• Components of Batteries

  • A battery contains two or more cells connected in series to produce a greater voltage 
  • The voltage produced by a cell is dependent on the type of electrode and type of electrolyte used
  • Cells joined in series can produce a higher voltage

  
• Non rechargeable batteries

  • In alkaline batteries, at some point the reactants in the batteries run out and no more electricity is produced
  • There is no way that we can reverse these reactions, so these are non-rechargeable batteries
• Rechargeable batteries

  • Rechargeable batteries can be recharged 
  • We can reverse the chemical reactions when we apply an electrical current