Edexcel Jun 2009 Paper 1 Q22 (with explained solutions) |

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Edexcel Jun 2009 Paper 1 Q22

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22 The Born-Haber cycle for the formation of sodium chloride from sodium and chlorine may be represented by a series of steps labelled A to F as shown. Na+(g) + Cl(g) Na+(g) + Cl(g) Na+(g) + Cl2(g) Na(g) + Cl2(g) Na(s) + Cl2(g) NaCl(s) 16 *H34471A01628*<br />
Energy change Letter Lattice energy for sodium chloride Enthalpy change of atomization of sodium Enthalpy change of atomization of chlorine First ionization energy of sodium First electron affinity of chlorine Enthalpy change of formation of sodium chloride (a) (i) Complete the table below by adding the letters A to F next to the corresponding energy changes. (3) H /kJ mol1 775 +109 +121 +494 411 (ii) Calculate the first electron affinity of chlorine, in kJ mol1, from the data given. (2) *H34471A01728* 17 Turn over<br />
(b) Lattice energies can be calculated from electrostatic theory (theoretical values) as well as by Born-Haber cycles (experimental values). Compound NaCl Agl Experimental lattice energy / kJ mol1 Theoretical lattice energy / kJ mol1 770 889 766 778 (i) Comment on the fact that there is close agreement between the values for sodium chloride, NaCl. (1)*(ii) Explain, in terms of chemical bonding, why the experimental value for silver iodide, AgI, is more exothermic than the value calculated theoretically for the same compound. (2)18 *H34471A01828*<br />
*(c) Suggest why the first ionization energies of the Group 1 elements decrease down the group. (2)(Total for Question 22 = 10 marks) *H34471A01928* 19 Turn over<br />

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Question Number 21 (d) Correct Answer Reject Mark Reject Mark Question Number 22 (a)(i) repeat unit (1) continuation bonds shown (but these bonds do not have to cut through the brackets) (1) n not essential IGNORE the position of n relative to the repeat unit (e.g. can be written as a superscript) Correct Answer Energy change Letter Lattice energy for sodium chloride Enthalpy change of atomization of sodium Enthalpy change of atomization of chlorine First ionization energy of sodium First electron affinity of chlorine Enthalpy change of formation of sodium chloride 6 correct letters (3) 5 or 4 correct letters (2) 3 or 2 correct letters (1) 1 or 0 correct letters (0) H/kJ mol-1 -775 +109 +121 +494 -411<br />
Question Number 22 (a)(ii) Question Number 22 (b)(i) Question Number 22 (b)(ii) QWC Correct Answer Expression such as: D = C + B + A + F + E - 411 = + 109 + 494 + 121 + F + ( - 775) F = - 411 - 109 - 494 - 121 + 775 (1) Answer: F = 360 (kJ mol-1) (1) Check empty box in 22(a)(i), as answer may be written there. Answer must follow from working Correct answer only (2) Correct answer with some consistent working (2) Correct Answer (Bonding in NaCl) 100% ionic OR almost completely ionic OR no covalent character/(very) little covalent character Correct Answer AgI has (a degree of) covalent character (1) due to polarization or distortion (of the anion) (1) Reject Mark Reject Molecule (0) Reject Mark Mark<br />
Question Number 22 (c) QWC Question Number 23 (a) Mark ions get bigger (down Group) Correct Answer Reject Any two of the following: (outermost) electron further from the nucleus/atoms get bigger/more shells (outermost) electron more shielded (by inner shells of e-) (force of) attraction between nucleus and (outermost) electron decreases (down the Group) OR (outermost) electron held less strongly (down the Group) OR (outermost) electron becomes easier to remove (down the Group) IGNORE any references to(effective) nuclear charge or more protons. Reject Mark Correct Answer element structure bonding sodium Giant metallic silicon Giant (atomic)/ macromolecular/ giant molecular covalent sulfur simple / small molecules OR (simple) molecular OR S8 molecules covalent or van der Waals forces/ London forces/ intermolecular forces/dispersion forces/induced- dipole forces IGNORE the word lattice OR crystalline 6 boxes correct (3) 5,4 boxes correct (2) 3,2 boxes correct (1) 1,0 boxes correct (0)<br />

Question 21 22 23 24

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