ENERGY CHANGES

ENERGY CHANGES

1. EXOTHERMIC

   • products have lower energy than reactants
   • measured in kilojoules
   • EG : neutralisation of an acid by alkali, combustion of fuels, reaction between iron & sulfur
   • energy given out
   • rise in temperature

2. ENDOTHERMIC

   • energy taken in
   • fall in temperature
   • product have HIGHER energy than reactants
   • measured in kilojoules
   • EG: thermal decompostion of Calcium Carbonate, photosynthesis, reaction that take place during cooking

3. MORE ON ENERGY CHANGES

   • In chemical reaction, bonds are broken, bonds are formed
   • Energy TAKEN IN for breaking bond (ENDOTHERMIC)
   • Energy RELEASED when bonds form (EXOTHERMIC)
   • energy taken in > energy given out = endothermic
   • energy taken in < energy given out = exothermic
   • amount of energy needed to break bonds is DIFFERENT from amount of energy given out by forming bonds

4. CALCULATING ENERGY CHANGE

   • use balanced equation
   • energy change = energy in - energy out
   • (-) shows EXOTHERMIC
   • (+) shows ENDOTHERMIC

5. ENERGY FROM FUELS

   • Substance we use as source of energy
   • FOSSIL FUELS
     • oil, natural gas, coal
     • burns oxygen in the air
     • Chemical energy is released as heat
     • in homes : cooking & heating
     • gas-fired power stations : boil water to make steam which generates electricity
     • combustion produces carbon dioxide = global warming
   • NUCLEAR FUELS
     • Radioisotopes
     • not burned, broken down by bombarding them with neutrons
     • Atomic energy released as heat
     • nuclear power stations : boils water to make steam which generates electricity
     • Harmful radiation
     • products are radioactive

6. CELLS

   • SIMPLE CELLS
     • consists of rods of two different metals (one metal gives up electrons more readily than the other) standing in an electrolyte
     • REDOX reactions provide a current
   • FUEL CELLS
     • hydrogen reacts with oxygen without combustion
     • at (-)pole :hydrogen is oxidised
     • at (+)pole: oxygen is reduced
     • used to provide electricity in spacecrafts
     • clean form of energy
     • used in some homes for electricity
     • being developed for transportation

7. REVERSIBLE REACTIONS

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