AQA Jun 2012 Paper 5 Q3 (with explained solutions) |

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AQA Jun 2012 Paper 5 Q3

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do not write outside the box some thermodynamic data for fluorine and chlorine are shown in the table in the table x represents the halogen f or cl electronegativity electron affinity kj mol enthalpy of atomisation kj mol enthalpy of hydration of x g kj mol fluorine chlorine a explain the meaning of the term electron affinity marks b explain why the electronegativity of fluorine is greater than the electronegativity of chlorine marks extra space c explain why the hydration enthalpy of the fluoride ion is more negative than the hydration enthalpy of the chloride ion marks wmp jun chem do not write outside the box d the enthalpy of solution for silver fluoride in water is kj mol the hydration enthalpy for silver ions is kj mol d i use these data and data from the table to calculate a value for the lattice enthalpy of dissociation of silver fluoride marks d ii suggest why the entropy change for dissolving silver fluoride in water has a positive value mark d iii explain why the dissolving of silver fluoride in water is always a spontaneous process marks turn over wmp jun chem

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mark scheme general certificate of education a level chemistry unit energetics redox and inorganic chemistry june marking guidance mark comments question a allow explanation with an equation that includes state symbols if ionisation ionisation energy implied ce for both marks ignore conditions fluorine molecules ions charge density ce for both marks any reference to electronegativity ce allow h on water do not allow o on water allow f hydrogen bonds to water chloride ion does not mark independently enthalpy change heat energy change when one mole of gaseous atoms form one mole of gaseous negative ions with a single charge b c fluorine atom is smaller than chlorine shielding is less outer electrons closer to nucleus bond pair of electrons attracted more strongly to the nucleus protons fluoride ions smaller than chloride have larger charge density so negative charge attracts hydrogen on water more strongly mark scheme general certificate of education a level chemistry unit energetics redox and inorganic chemistry june d i h solution le hydration enthalpies correct cycle le kj mol d ii there is an increase in the number of particles more disorder less order d iii entropy change is positive entropy increases and enthalpy change negative exothermic so g is always negative agf or other wrong formula ce ignore state symbols in cycle ignore no units penalise m for wrong units scores max mark out of loses m but m and m may be correct is transfer error ae scores marks max if m correct ce results from agf allow incorrect formulae and numbers provided number increases do not penalise reference to atoms molecules ignore incorrect reference to liquid rather than solution

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