School / IB / CHEMISTRY HL / Reactivity 1: entropy and spontaneity (HL) Question practice
Reactivity 1: entropy and spontaneity (HL) About this practice Born-Haber cycles, entropy and Gibbs free energy.
Chemistry HL Reactivity 1: entropy and spontaneity (HL)
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3 Construct a Born-Haber cycle for the formation of sodium chloride, NaCl(s), from its elements, listing the enthalpy terms needed: atomization of sodium, atomization of chlorine, first ionization energy of sodium, first electron affinity of chlorine, and lattice enthalpy. Medium 5 marks No calculator + 4 Marking analysis: A learner attempts the following task: “Construct a Born-Haber cycle for the formation of sodium chloride, NaCl(s), from its elements, listing the enthalpy terms needed: atomization of sodium, atomization of chlorine, first ionization energy of sodium, first electron affinity of chlorine, and lattice enthalpy.” Their response addresses only this point: “Includes enthalpy of atomization of sodium: Na(s) → Na(g).” Evaluate the response against the complete 5-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Medium 5 marks No calculator + 5 Using the Born-Haber cycle for NaCl (ΔHf = −411, atomization Na = +107, atomization Cl = +122, IE1 Na = +496, EA1 Cl = −349, all in kJ mol⁻¹), calculate the lattice enthalpy of NaCl. Medium 4 marks Calculator + 6 Marking analysis: A learner attempts the following task: “Using the Born-Haber cycle for NaCl (ΔHf = −411, atomization Na = +107, atomization Cl = +122, IE1 Na = +496, EA1 Cl = −349, all in kJ mol⁻¹), calculate the lattice enthalpy of NaCl.” Their response addresses only this point: “States Hess's law relation: ΔHf = ΔHatom(Na) + ΔHatom(Cl) + IE1(Na) + EA1(Cl) + ΔHlattice.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Medium 4 marks Calculator + 13 A reaction has ΔH = +58 kJ mol⁻¹ and ΔS = +176 J K⁻¹ mol⁻¹. Calculate the minimum temperature (in K) at which the reaction becomes spontaneous. Medium 4 marks Calculator + 14 Marking analysis: A learner attempts the following task: “A reaction has ΔH = +58 kJ mol⁻¹ and ΔS = +176 J K⁻¹ mol⁻¹. Calculate the minimum temperature (in K) at which the reaction becomes spontaneous.” Their response addresses only this point: “States that the reaction becomes spontaneous when ΔG = 0, i.e. the boundary condition ΔH = TΔS.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Medium 4 marks Calculator + 23 A reaction (the Haber process) has ΔH° = −92 kJ mol⁻¹ and ΔS° = −199 J K⁻¹ mol⁻¹ at 298 K. Calculate ΔG° for this reaction at 298 K, and state whether it is spontaneous under these conditions. Medium 4 marks Calculator + 24 Marking analysis: A learner attempts the following task: “A reaction (the Haber process) has ΔH° = −92 kJ mol⁻¹ and ΔS° = −199 J K⁻¹ mol⁻¹ at 298 K. Calculate ΔG° for this reaction at 298 K, and state whether it is spontaneous under these conditions.” Their response addresses only this point: “Converts ΔH° to consistent units: −92 000 J mol⁻¹.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Medium 4 marks Calculator + 29 Construct an enthalpy cycle relating the enthalpy of solution of an ionic compound to its lattice enthalpy (of dissociation) and the enthalpies of hydration of its ions, and hence state the equation linking these three enthalpies. Medium 4 marks No calculator + 30 Marking analysis: A learner attempts the following task: “Construct an enthalpy cycle relating the enthalpy of solution of an ionic compound to its lattice enthalpy (of dissociation) and the enthalpies of hydration of its ions, and hence state the equation linking these three enthalpies.” Their response addresses only this point: “States that dissolving an ionic solid in water can be considered in two steps: first, breaking apart the lattice into gaseous ions (lattice dissociation enthalpy, endothermic).” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Medium 4 marks No calculator + Self-assessed Not marked yet
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