Topic 12: Entropy and Energetics

Understand that, since endothermic reactions can occur spontaneously at room temperature, enthalpy changes alone do not control whether reactions occur.

Use —that, since endothermic reactions can occur spontaneously at room temperature, enthalpy changes alone do not control whether to connect the rule to the data and decision in the question.

This matters because —that, since endothermic reactions can occur spontaneously at room temperature, enthalpy changes alone do not control whether determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply —that, since endothermic reactions can occur spontaneously at room temperature, enthalpy changes alone do not control whether to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: —That, since endothermic reactions can occur spontaneously at room temperature, enthalpy changes alone do not control whether is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Understand entropy as a measure of disorder of a system in terms of the random dispersal of molecules and of energy quanta between molecules.

Use —entropy as a measure of disorder of a system in terms of the random dispersal of molecules and of energy quanta between to connect the rule to the data and decision in the question.

This matters because —entropy as a measure of disorder of a system in terms of the random dispersal of molecules and of energy quanta between determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply —entropy as a measure of disorder of a system in terms of the random dispersal of molecules and of energy quanta between to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: —Entropy as a measure of disorder of a system in terms of the random dispersal of molecules and of energy quanta between is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Understand that the entropy of a substance increases with temperature, that entropy increases as solid → liquid → gas and that perfect crystals at zero kelvin have zero entropy.

Use —the entropy of a substance increases with temperature, that entropy increases as solid → liquid → gas and that perfect to connect the rule to the data and decision in the question.

This matters because —the entropy of a substance increases with temperature, that entropy increases as solid → liquid → gas and that perfect determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply —the entropy of a substance increases with temperature, that entropy increases as solid → liquid → gas and that perfect to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: —The entropy of a substance increases with temperature, that entropy increases as solid → liquid → gas and that perfect is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Be able to interpret the natural direction of change as being in the direction of increasing total entropy (positive entropy change), including gases spread spontaneously through a room.

Use —interpret the natural direction of change as being in the direction of increasing total entropy (positive entropy change) to connect the rule to the data and decision in the question.

This matters because —interpret the natural direction of change as being in the direction of increasing total entropy (positive entropy change) determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply —interpret the natural direction of change as being in the direction of increasing total entropy (positive entropy change) to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: —Interpret the natural direction of change as being in the direction of increasing total entropy (positive entropy change) is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Understand why entropy changes occur during: i changes of state ii dissolving of a solid ionic lattice iii reactions in which there is a change in the number of moles from reactants to products.

Use —why entropy changes occur during: i changes of state ii dissolving of a solid ionic lattice iii reactions in which there is to connect the rule to the data and decision in the question.

This matters because —why entropy changes occur during: i changes of state ii dissolving of a solid ionic lattice iii reactions in which there is determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply —why entropy changes occur during: i changes of state ii dissolving of a solid ionic lattice iii reactions in which there is to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: —Why entropy changes occur during: i changes of state ii dissolving of a solid ionic lattice iii reactions in which there is is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Understand that the total entropy change of any reaction is the sum of the entropy change of the system and the entropy change of the surroundings, summarised by the expression: ∆Stotal = ∆Ssystem + ∆Ssurroundings.

Use —the total entropy change of any reaction is the sum of the entropy change of the system and the entropy change of to connect the rule to the data and decision in the question.

This matters because —the total entropy change of any reaction is the sum of the entropy change of the system and the entropy change of determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply —the total entropy change of any reaction is the sum of the entropy change of the system and the entropy change of to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: —The total entropy change of any reaction is the sum of the entropy change of the system and the entropy change of is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Be able to calculate the entropy change of the system for a reaction, ∆Ssystem, given the entropies of the reactants and products.

Use —the entropy change of the system for a reaction, ∆ssystem, given the entropies of the reactants and products to connect the rule to the data and decision in the question.

This matters because —the entropy change of the system for a reaction, ∆ssystem, given the entropies of the reactants and products determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply —the entropy change of the system for a reaction, ∆ssystem, given the entropies of the reactants and products to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: —The entropy change of the system for a reaction, ∆Ssystem, given the entropies of the reactants and products is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Be able to calculate the entropy change in the surroundings, and hence ∆Stotal, using the expression ∆Ssurroundings = −∆H T.

Use —the entropy change in the surroundings, and hence ∆stotal to connect the rule to the data and decision in the question.

This matters because —the entropy change in the surroundings, and hence ∆stotal determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply —the entropy change in the surroundings, and hence ∆stotal to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: —The entropy change in the surroundings, and hence ∆Stotal is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Understand that the feasibility of a reaction depends on: i the balance between ∆Ssystem and ∆Ssurroundings, so that even endothermic reactions can occur spontaneously at room temperature ii temperature, as higher temperatures decrease the magnitude of ∆Ssurroundings so its contribution to ∆Stotal is less Students should be able to calculate the temperature at which a reaction is feasible. Students may also use ∆G = ∆H - T∆Ssystem in answers, although this approach is not a requirement of the specification.

Use —the feasibility of a reaction depends on: i the balance between ∆ssystem and ∆ssurroundings, so that even endothermic to connect the rule to the data and decision in the question.

This matters because —the feasibility of a reaction depends on: i the balance between ∆ssystem and ∆ssurroundings, so that even endothermic determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply —the feasibility of a reaction depends on: i the balance between ∆ssystem and ∆ssurroundings, so that even endothermic to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: —The feasibility of a reaction depends on: i the balance between ∆Ssystem and ∆Ssurroundings, so that even endothermic is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Understand that reactions can occur as long as ∆Stotal is positive even if one of the other entropy changes is negative.

Use —reactions can occur as long as ∆stotal is positive even if one of the other entropy changes is negative to connect the rule to the data and decision in the question.

This matters because —reactions can occur as long as ∆stotal is positive even if one of the other entropy changes is negative determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply —reactions can occur as long as ∆stotal is positive even if one of the other entropy changes is negative to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: —Reactions can occur as long as ∆Stotal is positive even if one of the other entropy changes is negative is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Understand and distinguish between the concepts of thermodynamic stability and kinetic stability.

Use —and distinguish between the concepts of thermodynamic stability and kinetic stability to connect the rule to the data and decision in the question.

This matters because —and distinguish between the concepts of thermodynamic stability and kinetic stability determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply —and distinguish between the concepts of thermodynamic stability and kinetic stability to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: —And distinguish between the concepts of thermodynamic stability and kinetic stability is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Be able to define the terms: i standard enthalpy change of atomisation, ∆atH ii electron affinity iii lattice energy (as the exothermic process for the formation of one mole of an ionic solid from its gaseous ions).

Use —define the terms: i standard enthalpy change of atomisation, ∆ath ii electron affinity iii lattice energy (as the exothermic to connect the rule to the data and decision in the question.

This matters because —define the terms: i standard enthalpy change of atomisation, ∆ath ii electron affinity iii lattice energy (as the exothermic determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply —define the terms: i standard enthalpy change of atomisation, ∆ath ii electron affinity iii lattice energy (as the exothermic to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: —Define the terms: i standard enthalpy change of atomisation, ∆atH ii electron affinity iii lattice energy (as the exothermic is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Be able to construct Born-Haber cycles and carry out related calculations.

Use —construct born-haber cycles and carry out related calculations to connect the rule to the data and decision in the question.

This matters because —construct born-haber cycles and carry out related calculations determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply —construct born-haber cycles and carry out related calculations to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: —Construct Born-Haber cycles and carry out related calculations is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Understand that a comparison of the experimental lattice energy value (from a Born-Haber cycle) with the theoretical value (obtained from electrostatic theory) in a particular compound indicates the degree of covalent bonding.

Use —a comparison of the experimental lattice energy value (from a born-haber cycle) with the theoretical value (obtained to connect the rule to the data and decision in the question.

This matters because —a comparison of the experimental lattice energy value (from a born-haber cycle) with the theoretical value (obtained determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply —a comparison of the experimental lattice energy value (from a born-haber cycle) with the theoretical value (obtained to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: —A comparison of the experimental lattice energy value (from a Born-Haber cycle) with the theoretical value (obtained is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Understand that polarisation of anions by cations leads to some covalency in an ionic bond, based on evidence from the Born-Haber cycle.

Use —polarisation of anions by cations leads to some covalency in an ionic bond, based on evidence from the born-haber cycle to connect the rule to the data and decision in the question.

This matters because —polarisation of anions by cations leads to some covalency in an ionic bond, based on evidence from the born-haber cycle determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply —polarisation of anions by cations leads to some covalency in an ionic bond, based on evidence from the born-haber cycle to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: —Polarisation of anions by cations leads to some covalency in an ionic bond, based on evidence from the Born-Haber cycle is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Be able to define the terms ‘enthalpy change of solution, ∆solH’ and ‘enthalpy change of hydration, ∆hydH of an ion’.

Use —define the terms ‘enthalpy change of solution, ∆solh’ and ‘enthalpy change of hydration, ∆hydh of an ion’ to connect the rule to the data and decision in the question.

This matters because —define the terms ‘enthalpy change of solution, ∆solh’ and ‘enthalpy change of hydration, ∆hydh of an ion’ determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply —define the terms ‘enthalpy change of solution, ∆solh’ and ‘enthalpy change of hydration, ∆hydh of an ion’ to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: —Define the terms ‘enthalpy change of solution, ∆solH’ and ‘enthalpy change of hydration, ∆hydH of an ion’ is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Be able to use energy cycles and energy level diagrams to calculate the enthalpy change of solution of an ionic compound, using enthalpy change of hydration and lattice energy.

Use —energy cycles and energy level diagrams to calculate the enthalpy change of solution of an ionic compound to connect the rule to the data and decision in the question.

This matters because —energy cycles and energy level diagrams to calculate the enthalpy change of solution of an ionic compound determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply —energy cycles and energy level diagrams to calculate the enthalpy change of solution of an ionic compound to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: —Energy cycles and energy level diagrams to calculate the enthalpy change of solution of an ionic compound is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Understand the effect of ionic charge and ionic radius on the values of enthalpy change of hydration and the lattice energy of an ionic compound.

Use —the effect of ionic charge and ionic radius on the values of enthalpy change of hydration and the lattice energy of an ionic to connect the rule to the data and decision in the question.

This matters because —the effect of ionic charge and ionic radius on the values of enthalpy change of hydration and the lattice energy of an ionic determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply —the effect of ionic charge and ionic radius on the values of enthalpy change of hydration and the lattice energy of an ionic to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: —The effect of ionic charge and ionic radius on the values of enthalpy change of hydration and the lattice energy of an ionic is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Be able to use entropy and enthalpy changes of solution values to predict the solubility of ionic compounds and discuss trends in the solubility of ionic compounds covered in Unit 2.

Use —entropy and enthalpy changes of solution values to predict the solubility of ionic compounds and discuss trends in to connect the rule to the data and decision in the question.

This matters because —entropy and enthalpy changes of solution values to predict the solubility of ionic compounds and discuss trends in determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply —entropy and enthalpy changes of solution values to predict the solubility of ionic compounds and discuss trends in to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: —Entropy and enthalpy changes of solution values to predict the solubility of ionic compounds and discuss trends in is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.