Energy changes

• exothermic

  energy released into surroundings

  ex => exit

  On reaction profile the reactants will be higher than products

  e.g combustion reactions and neutralisation and oxidation
• Endothermic

  take in energy from surroundings

  en => enter

  On reaction profile reactants are lower than the products
• Activation energy

  -Minimum amount of energy the reactants particles need in order collide with each other and react

  -difference between reactants energy level and the top of the curve
• Bond energy

  Amount of energy required to break one mole of a particular covalent bond
• Overall energy change in reaction

  (Energy to break bonds) - (energy to form bonds)
• Cells + batteries


  Voltage increase if difference in reactivity of metals is larger, or concentration or temperature
• Batteries


  Rechargeable = reversible reaction by electrical current

  non rechargeable = reaction stops when reactions used up (alkaline batteries)
• fuel cell


  Electrochemical cell converts energy between electrical and chemical
• Hydrogen-oxygen fuel cell


  -Combines hydrogen and oxygen to create water + energy

  -anode = negative & cathode = positive (opposite to electrolysis) and made of pours carbon + catalyst

  -hydrogen enters by anode and oxygen enters by cathode

  -water and heat leave via outlet by cathode
• Hydrogen-oxygen cells


  -hydrogen enters by the anode and is oxidised (loses electrons)

  H2 => 2(H+) + 2e-

  -hydrogen passes through to the cathode

  -oxygen can react with H and electrons at the cathode and combine to make water

  O2 + 4(H+) + 4e- => 2(H2O)

  -water leaves via outlet
• Pros & cons


  + only require H and O2 which are abundant

  + not polluting

  + simple devices

  + less polluting when disposed of

  -more space to store

  -explosive if mixed with air

  -to make H it requires energy e.g fossil fuels