Salters A level advanced chemistry, Df4 topic, " where does energy come from ?".
James Howlett
Mind Map by James Howlett, updated more than 1 year ago
James Howlett
Created by James Howlett over 8 years ago

Resource summary

  1. Bond enthalpies
    1. Chemical bond = electrical attraction between atoms or ions
      1. Bond enthalpy = Qunatity of energy required to break a particular bond in a molecule
        1. Bond enthalpy will be a negative value if exothermic
          1. Greater the bond enthalpy the stronger the bond
            1. Equilibrium bond length = Attractive and opposing forces with in bond are equal
              1. Shorter bond length = stronger bond
              2. Double bond = high B.E Triple bond = V.high B.E
                1. Average bond enthalpies used; exact value is dependent on particular compound bond is found.
                  1. Bond enthalpies measured indirectly using enthalpy cycles
                  2. Usefull links
                    1. http://www.lisgar.net/magwood/sch4u%20bonding%203.htm
                      1. http://www.chemguide.co.uk/physical/energetics/sums.html
                      2. Breaking and making bonds
                        1. CH4 + 2 O2 = CO2 + 2 H2O
                          1. ΔH = -890 KJmolmol-1
                            1. Is breaking bonds and creating new ones
                              1. Worked out by looking at structure of reactants and products
                            2. Always refers to breaking a bond in a gaseous compound
                              1. Combustion of methane = exothermic
                                1. energy in bond-breaking steps < energy in bond-making
                                2. Not all have to be broken to form new ones
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