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DP IB Chemistry: SL

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Home / IB / Chemistry: SL / DP / Topic Questions / 5. Energetics / Thermochemistry / 5.2 Hess's Law / Structured Questions: Paper 2


5.2 Hess's Law

Question 1a

Marks: 1
a)
State Hess’s Law.
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    Key Concepts
    Hess's Law

    Question 1b

    Marks: 1
    b)
    State the type of system in which the total amount of matter present is always constant. 

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      Key Concepts
      Hess's Law

      Question 1c

      Marks: 1
      c)
      Using the image below, construct an equation that can be used to determine ΔHr from ΔH1 and  ΔH2.

      5-2-ib-sl-sq-easy-q1c-hesss-law-cycle

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        Key Concepts
        Hess's Law

        Question 1d

        Marks: 3
        d)
        Complete the following Hess’s Law cycle for the decomposition of copper carbonate.
        5-2-ib-sl-sq-easy-q1d-hesss-law-cycle-cuco3

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          Question 2a

          Marks: 2
          a)
          Define standard enthalpy of formation, ΔHf

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            Question 2b

            Marks: 8
            b)
            Write an equation to show the enthalpy of formation of 1 mole of the following compounds. Include state symbols in your equations. 
            Methanol, CH3OH ………………………………..
            Carbon dioxide, CO………………………………..
            Ethane, C2H………………………………..
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              Question 2c

              Marks: 3
              c)
              Using the equations given, construct a Hess’s Law cycle for the following reaction. Include the values for ΔHf  in your cycle.  

              BaCl2 (s) + Zn (s) → Ba (s) + ZnCl(s)

                 Ba (s) + Cl2 (g) → BaCl(s)      ΔHf = -858.6 kJ mol-1

                 Zn (s) + Cl2 (g) → ZnCl2 (s)         ΔHf = -415.1 kJ mol-1

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                Question 2d

                Marks: 3
                d)
                Calculate the enthalpy of reaction, ΔHrfor the reaction given in part (c).

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                  Question 3a

                  Marks: 4
                  a)
                  Aluminium oxide reacts with magnesium to form magnesium oxide and aluminium in a displacement reaction via the following reaction.
                  Construct a Hess’s Law cycle for this reaction

                  Al2O3 (s) + 3Mg (s) → 3MgO (s) + 2Al (s)

                   

                  Enthalpy of formation Enthalpy of formation (kJ mol-1)
                  ΔHf (Al2O3) -1675.7 
                  ΔHf (MgO) -601.7 
                  ΔHf (Mg)  
                  ΔHf (Al)  

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                    Question 3b

                    Marks: 1
                    b)
                    Outline why no values are listed for Al (s) and Mg (s) in the table given in part (a).
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                      Question 3c

                      Marks: 2
                      c)
                      Calculate the enthalpy change of reaction, ΔHr, for the reaction in part (a).
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                        Question 4a

                        Marks: 3
                        a)
                        Determine the enthalpy change of reaction, ΔHr, for the following equations if they are reversed. 

                        2Na + Cl2 → 2NaCl           ΔHr = -790 kJ ……………………….

                        C2H+ H2 → C2H6               ΔHr = -65.6 kJ ………………………

                        2H2O → 2H+ O2             ΔH= +571 kJ ……………………….

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                          Question 4b

                          Marks: 1
                          b)
                          Using the information given in part (a), determine the enthalpy change for the following reaction.

                          2C2H4 + 2H2 → 2C2H6

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                            Question 4c

                            Marks: 1
                            c)
                            Using the information in the table, deduce which equation should be reversed to determine the enthalpy change for the following reaction. 

                            SiO2 + 3C → SiC + 2CO

                            Equation number  Equation Enthalpy change (kJ)
                            1 Si + O2 → SiO2 -911
                            2 2C + O2 → 2CO -211
                            3 Si + C → SiC -65.3

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                              Question 4d

                              Marks: 2
                              d)
                              Use the information in part (c) to produce an overall cancelled down equation which can be used to determine the overall enthalpy change for the following reaction. 

                              SiO2 + 3C → SiC + 2CO

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                                Question 4e

                                Marks: 2
                                e)
                                Deduce the overall enthalpy change, in kJ, using the information in part (c) for the reaction SiO2 + 3C → SiC + 2CO
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                                  Question 5a

                                  Marks: 1
                                  a)
                                  State the equation required to calculate the enthalpy change of reaction, ΔHr, given enthalpy of formation, ΔHf, data. 

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                                    Question 5b

                                    Marks: 3
                                    b)
                                    Using section 12 in the data booklet and the data in the table calculate the enthalpy change of reaction, ΔHr, for the following reaction.

                                    SO2 (g) + 2H2S (g) → 3S (s) + 2H2O (l) 

                                      SO2 (g) H2S (g)
                                    ΔHf (kJ mol-1 -297 -20.2
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                                      Question 5c

                                      Marks: 2
                                      c)
                                      Show how the equations can be used to produce an alternative route for this reaction.

                                      C2H4 + H2 → C2H6

                                        ΔH (kJ mol-1)
                                      C2H4 + 3O2 → 2CO2 + 2H2O -1411
                                      C2H6 + 3½O2 2CO(g) + 3H2O -1560
                                      H2 + ½O2 → H2O -285.8

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                                        Question 5d

                                        Marks: 1
                                        d)
                                        Calculate ΔH
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