Chemistry

• Energy is conserved in a chemical reaction
• Exothermic reactions release energy to the surroundings
• Endothermic reactions absorb energy from surroundings
• Exothetmic reactions include combustion, oxidation and neutralisation
• Endothermic reactions include thermal decomposition
• An example of exothermic would be self heating cans and hand warmers
• An example of endothermic is sports injury packs
• Exothermic reactions causes surroundings to increase in temp
• Endothermic reactions cause surroundings to decrease in temp
• Bond breaking absorbs energy
• Bond making releases energy
• BB < BM is exothermic
• BB > BM is endothermic
• Chemical reactions can only occur when reacting particles collide with each other
• Delta h is the difference in energy levels between the products and reactants
• Negative delta h is exothermic
• Positive delta h is endothermic
• Simple cells can be made by connecting 2 different metals in contact with an electrolyte
• Hydrogen fuel cells at negative electrode

  2H2 + 4OH- -> 4H2O + 4e-
• Hydrogen fuel cells at positive electrode

  O2 + 2H2O + 4e- -> 4OH-
• Hydrogen fuel cell overall equation

  2H2 + O2 -> 2H2O
• The voltage produced by a cell is dependent upon the type of electron and electrolyte
• Type of electron

  Different metals will react differently with the same electrolyte
• electrolyte used

  Different ions in solution with react differently with the metal electrodes used
• How many cells you use

  A battery is formed by connecting two or more cells together in series . The voltage of the individual cells combine together so there is a bigger overall voltage
• RP - temperature change

  1)put 30 cm3 of hydrochloric acid in a polystyrene cup

  2)stand the cup in a beaker

  3) measure the temp of the acid

  4)measure 5cm3 of sodium hydroxide and pour into the cup

  5)put the lid on and stir the solution with the thermometer

  6) record the temp then the temp stops changing

  7)repeat steps 4-6 until a total of 40 cm 3 of sodium hydroxide has been added

  8)rinse the cup and repeat 2 more times