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Energy Changes (Bond energies (Calculations (can't compare overall…

- - - - relative energies of reactants and products
      - energy changes over course of reaction
    - - product at lower energy than reactant
      - difference in height is overall energy change
      - activation energy, is initial energy
        to break old bonds and start reaction
        
        minimum energy need for reactants
        to collide with each other and react
        
        needs to be supplied, e.g by heating
    - - products at higher energy than reactant
      - Difference in height is enery change (energy taken in)
  - - - Br-Br weaker than Cl-Cl and H-Br weaker than H-Cl
- - - - Heat given out, increase in temperature
      - E.g
        
        burning fuels, called combustion, very exothermic
        
        Neutralisation reactions
        
        many oxidation, eg Na in water, releases
        energy, and Na moves in the water
      - Every day uses
        
        Come hand warmers use this with iron in
        air (with salt solution catalyst) to release energy.
        
        self heating cans of hot chocolate, coffee,
        from chemicals in their bases
    - - less common than exothermic
      - take in energy, fall in temperature
      - E.g
        
        citric acid and sodium hydroencarbonate
        
        thermal decompostion e.g Calcium carbonate
        to CaO (quicklime) & CO2
      - Every day use - sport injury packs, instantly
        cooler without putting in freezer