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DP IB Chemistry: SL

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Home / IB / Chemistry: SL / DP / Topic Questions / 5. Energetics / Thermochemistry / 5.3 Bond Enthalpy / Structured Questions: Paper 2


5.3 Bond Enthalpy

Question 1a

Marks: 2
a)
During chemical reactions, enthalpy changes occur as bonds are broken and formed.

i)
Thermal energy is needed to overcome the attractive forces between atoms. In terms of thermal energy, name the process where bonds are broken.

ii)
When bonds are formed, thermal energy is released to the surroundings. In terms of thermal energy, name the process where bonds are made.
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    Key Concepts
    Bonds & Energy

    Question 1b

    Marks: 5
    b)
    The energy level diagram for an endothermic reaction is shown below.

    1-19

       Complete the diagram by labelling parts A to E. 

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      Key Concepts
      Energy profiles

      Question 1c

      Marks: 1
      c)
      An element X undergoes complete combustion according to the following equation. The enthalpy change, ΔH, and activation energy, Ea, for this reaction are -520 kJ mol-1 and +630 kJ mol-1 respectively. Deduce whether this reaction is exothermic or endothermic. 

      X + O2 → XO2

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        Key Concepts
        Energy profiles

        Question 1d

        Marks: 2
        d)
        Define the term average bond enthalpy.

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          Key Concepts
          Bond enthalpy

          Question 2a

          Marks: 1
          a)
          State the formula for calculating the standard enthalpy change of reaction, ΔHr, using bond energies.
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            Question 2b

            Marks: 4
            b)
            Use section 11 of the data booklet to calculate the enthalpy change, in kJ mol-1, for the following reaction.    

            Cl2 + H2 → 2HCl 

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              Question 2c

              Marks: 1
              c)
              State whether the energy change for the reaction in part (b) is endothermic or exothermic.

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                Question 2d

                Marks: 4
                d)
                Using section 11 of the data booklet, calculate the enthalpy change of reaction, ΔHr, in kJ mol-1 for the following reaction.

                CH4 + Cl2 → CH3Cl + HCl 

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                  Question 3a

                  Marks: 2
                  a)
                  Draw the Lewis structure of an oxygen molecule, O2.

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                    Question 3b

                    Marks: 1
                    b)
                    State the type of energy in the stratosphere responsible for the break down of the oxygen molecule. 

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                      Question 3c

                      Marks: 2
                      c)
                      State the equation for the formation of ozone and whether this reaction is endothermic or exothermic.

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                        Question 3d

                        Marks: 1
                        d)
                        State the name of the type of compound that is responsible for the disruption of the temperature regulation in the stratosphere.

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                          Question 4a

                          Marks: 2
                          a)
                          Using displayed formulae, write the equation for the reaction of ethene with water to form ethanol.

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                            Question 4b

                            Marks: 4
                            b)
                            Using section 11 in the data booklet calculate the enthalpy change of reaction, ΔHr, for the reaction of ethene with water. 

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                              Question 4c

                              Marks: 1
                              c)
                              Define bond dissociation energy.
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                                Key Concepts
                                Bond enthalpy