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DP IB Chemistry: SL

Topic Questions

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)
Define the term average bond enthalpy.
[2]
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    Key Concepts
    Bond enthalpy

    Question 1b

    Marks: 3
    b)
    Determine the bond dissociation energy, in kJ mol-1, for one mole of O−F bonds using the following equation and section 11 of the data booklet. Give your answer to 3 significant figures. 

    F(g) + ½O(g) → OF2 (g)    ΔHr = +28 kJ mol-1

    [3]

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      Question 1c

      Marks: 2
      c)
      The reaction of ethanoyl chloride, CH3COCl , and ethanol form an ester. State the equation for this reaction.
      [2]

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        Key Concepts
        Esterification

        Question 1d

        Marks: 2
        d)
        Use section 11 in the data booklet to deduce the energy required, in kJ mol-1, to break the bonds.
        [2]
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          Question 1e

          Marks: 3
          e)
          Deduce the energy released, in kJ mol-1, when the bonds are formed and therefore the enthalpy change for the reaction.
          [3]

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            Question 2a

            Marks: 2
            a)
            Methane reacts violently with fluorine to form carbon tetrafluoride and hydrogen fluoride

            Formulate the equation for this reaction. 
            [2]
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              Key Concepts
              Balancing Equations

              Question 2b

              Marks: 4
              b)
              Use your answer to part a) and section 10 of the data booklet to calculate the following:

              i)
              The energy required, in kJ, to break the bonds for the reaction between methane and fluorine.
              [1]
              ii)
              The energy released, in kJ, to form the bonds for the reaction between methane and fluorine.
              [1]
              iii)
              The enthalpy change, ΔHr, in kJ mol-1 for this reaction. 
              [2]

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                Question 2c

                Marks: 2
                c)
                A student suggested that one reason for the high reactivity of fluorine is a weak F−F bond. State whether the student is correct. Justify your answer. 
                [2]
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                  Key Concepts
                  Bond enthalpy

                  Question 2d

                  Marks: 3
                  d)
                  Sketch a labelled energy diagram for the reaction of methane and fluorine.
                  [3]

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                    Key Concepts
                    Energy profiles

                    Question 3a

                    Marks: 2
                    a)
                    Hydrazine has the formula N2H4 and is used as a rocket fuel (e.g. for the Apollo moon rockets). It burns in the following reaction for which the enthalpy change is -583 kJ mol-1.
                    N2H4 (g) + O2 (g) → N2 (g) + 2H2O (g)

                    Sketch the Lewis structure of hydrazine, N2H4.
                    [2]
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                      Key Concepts
                      Lewis structures

                      Question 3b

                      Marks: 3
                      b)
                      Use section 11 of the Data booklet and the information in part a) to deduce the bond enthalpy, in kJ mol-1, for the N-N bond.
                      [3]

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                        Question 3c

                        Marks: 1
                        c)
                        Outline why the value of enthalpy of reaction calculated from bond enthalpies is less accurate.
                        [1]
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                          Key Concepts
                          Bond enthalpy

                          Question 4a

                          Marks: 3
                          a)
                          Ozone prevents UV radiation emitted from the Sun reaching the surface of the Earth. Draw the resonance Lewis structures of ozone. 

                          [3]

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                            Question 4b

                            Marks: 4
                            b)
                            By using equations, state the environmental impact of CFCs on the ozone layer. 

                            [4]
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                              Question 4c

                              Marks: 3
                              c)
                              The destruction of ozone is a significant environmental issue as ozone can absorb frequencies of ultraviolet radiation that oxygen can not. 

                              Explain with reference to the structure and bonding of oxygen and ozone why this occurs. 
                              [3]
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