cells and batteries

• chemical reactions in a cell...


  produce electricity
• electrochemical cells


  produce electricity with a spontaneous redox reaction
• redox reaction


  a chemical reaction involving the transfer of one or more electrons from one reactant to another; also called oxidation-reduction reaction, where both oxidation and reduction are taking place
• oxidation reaction


  loss of electrons
• reduction reaction


  gain of electrons
• different metals will react differently...

  with the same electrolytes
• electrolyte


  a substance that dissolves in water to give a solution that conducts electric current because it contains ions
• electrode


  a metal strip that conducts electricity
• cathode


  - the electrode at which reduction occurs

  - negatively charged electrode

  - electrons flow into here
• anode


  - the electrode at which oxidation occurs

  - positively charged electrode

  - electrons flow from here
• half equations


  show reactions at the electrodes and what happens when ions gain or lose electrons
• cathode reactions


  positively charged ions gain electrons at the cathode

  - Na+ + e- → Na

  - Pb2+ + 2e- → Pb

  - 2H+ + 2e- → H2
• anode reactions


  negatively charged ions lose electrons at the anode

  - 2Cl- → Cl2 + 2e-

  - 2O2- → O2 + 4e-
• the bigger the difference in reactivity of the electrodes...

  the bigger the voltage of the cell
• voltmeter


  A device used to measure voltage, or electrical potential energy difference
• in non-rechargable batteries...


  the reactants get used up, since the reaction is irreversible
• fuel cell


  an electrical-chemical cell that converts fuel, such as hydrogen, and oxygen (or air) into an electrical current by using energy from the reaction between them
• in rechargable batteries...


  the reaction is reversible, meaning the reactants can be used again
• fuel cells use ... to produce electricity

  fuel and oxygen
• when fuel enters the fuel cell...

  it becomes oxidised and sets up potential difference within the cell
• hydrogen oxygen fuel cells...


  combine hydrogen and oxygen to produce clean water and energy
• fuel cell advantages


  - quiet

  - low maintenance (no moving parts)

  - fairly compact

  - waste water produced can be used for drinking/other purposes

  - waste heat is used for steam

  - more than 80% efficient

  - direct conversion

  - unlimited supplied
• fuel cell disadvantages


  - requires continuous supply

  - expensive

  - greenhouse gases are still produced

  - most operate at high temperatures
• non-rechargeable battery advantages


  - cheaper in the short term

  - largely insensitive to heat/cold

  - last longer (without needing to be recharged)

  - no expensive accessories, such as a charger, are required for their use
• non-rechargeable battery disadvantages


  - can only be used once

  - more expensive in the long term

  - not environmentally friendly, increased landfill waste
• rechargeable battery advantages


  - reusable, rechargeable

  - designed for long term use

  - cheaper for the long term

  - environmentally friendly, reduced landfill waste
• rechargeable battery disadvantages


  - more expensive

  - stores less energy

  - more expensive for the short term

  - limit to how often it can be recharged
• fossil fuels are...


  - non-renewable

  - very polluting
• batteries store ... energy than fuel cells

  more