ENERGY CHANGES

EXOTHERMIC
1. products have lower energy than reactants
2. measured in kilojoules
3. EG : neutralisation of an acid by alkali, combustion of fuels, reaction between iron & sulfur
4. energy given out
5. rise in temperature
ENDOTHERMIC
1. energy taken in
2. fall in temperature
3. product have HIGHER energy than reactants
4. measured in kilojoules
5. EG: thermal decompostion of Calcium Carbonate, photosynthesis, reaction that take place during cooking
MORE ON ENERGY CHANGES
1. In chemical reaction, bonds are broken, bonds are formed
2. Energy TAKEN IN for breaking bond (ENDOTHERMIC)
3. Energy RELEASED when bonds form (EXOTHERMIC)
4. energy taken in > energy given out = endothermic
5. energy taken in < energy given out = exothermic
6. amount of energy needed to break bonds is DIFFERENT from amount of energy given out by forming bonds
CALCULATING ENERGY CHANGE
1. use balanced equation
2. energy change = energy in - energy out
3. (-) shows EXOTHERMIC
4. (+) shows ENDOTHERMIC
ENERGY FROM FUELS
1. Substance we use as source of energy
2. FOSSIL FUELS
  1. oil, natural gas, coal
  2. burns oxygen in the air
  3. Chemical energy is released as heat
  4. in homes : cooking & heating
  5. gas-fired power stations : boil water to make steam which generates electricity
  6. combustion produces carbon dioxide = global warming
3. NUCLEAR FUELS
  1. Radioisotopes
  2. not burned, broken down by bombarding them with neutrons
  3. Atomic energy released as heat
  4. nuclear power stations : boils water to make steam which generates electricity
  5. Harmful radiation
  6. products are radioactive
CELLS
1. SIMPLE CELLS
  1. consists of rods of two different metals (one metal gives up electrons more readily than the other) standing in an electrolyte
  2. REDOX reactions provide a current
2. FUEL CELLS
  1. hydrogen reacts with oxygen without combustion
  2. at (-)pole :hydrogen is oxidised
  3. at (+)pole: oxygen is reduced
  4. used to provide electricity in spacecrafts
  5. clean form of energy
  6. used in some homes for electricity
  7. being developed for transportation
REVERSIBLE REACTIONS

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	Creado por iamawesomelyepic hace casi 11 años