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Questions and Answers
What is the enthalpy change called when 1 mole of an ionic compound is dissolved in water?
What is the enthalpy change called when 1 mole of an ionic compound is dissolved in water?
What is the enthalpy change called when the ions in an ionic lattice separate from each other?
What is the enthalpy change called when the ions in an ionic lattice separate from each other?
What equation represents the enthalpy of hydration for sodium ions?
What equation represents the enthalpy of hydration for sodium ions?
Which enthalpy change is always endothermic?
Which enthalpy change is always endothermic?
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Why is AgBr more covalent than NaBr?
Why is AgBr more covalent than NaBr?
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Which of these is a possible application of Hess's Law?
Which of these is a possible application of Hess's Law?
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Why is the enthalpy of solution sometimes exothermic and sometimes endothermic?
Why is the enthalpy of solution sometimes exothermic and sometimes endothermic?
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What is the enthalpy change called when an ion forms electrostatic attractions with water molecules?
What is the enthalpy change called when an ion forms electrostatic attractions with water molecules?
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Which of the following ions would have the most negative enthalpy of hydration?
Which of the following ions would have the most negative enthalpy of hydration?
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What is the relationship between the enthalpy of solution (ΔHsol) and the solubility of a salt in water?
What is the relationship between the enthalpy of solution (ΔHsol) and the solubility of a salt in water?
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Which of the following statements is TRUE regarding the lattice dissociation enthalpy (ΔHlatt diss) of ionic compounds?
Which of the following statements is TRUE regarding the lattice dissociation enthalpy (ΔHlatt diss) of ionic compounds?
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Which of the following factors would increase the entropy of a chemical system?
Which of the following factors would increase the entropy of a chemical system?
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If the enthalpy of solution for a salt is positive, what can be concluded about its solubility?
If the enthalpy of solution for a salt is positive, what can be concluded about its solubility?
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Which of the following is NOT a factor that affects the enthalpy of hydration?
Which of the following is NOT a factor that affects the enthalpy of hydration?
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What is the relationship between the enthalpy of lattice dissociation and the lattice enthalpy?
What is the relationship between the enthalpy of lattice dissociation and the lattice enthalpy?
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Which of the following statements accurately describes the enthalpy of solution?
Which of the following statements accurately describes the enthalpy of solution?
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What is the enthalpy change when one mole of an ionic substance dissociates fully into gaseous ions?
What is the enthalpy change when one mole of an ionic substance dissociates fully into gaseous ions?
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Which statement best describes the Enthalpy of Lattice Association?
Which statement best describes the Enthalpy of Lattice Association?
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What can be inferred about the enthalpy values for an ionic compound?
What can be inferred about the enthalpy values for an ionic compound?
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Which factor does NOT influence the strength of attraction between ions?
Which factor does NOT influence the strength of attraction between ions?
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For NaCl, what is the value of the Enthalpy of Lattice Dissociation?
For NaCl, what is the value of the Enthalpy of Lattice Dissociation?
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What occurs during the process of lattice dissociation?
What occurs during the process of lattice dissociation?
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Why is the Enthalpy of Lattice Association negative?
Why is the Enthalpy of Lattice Association negative?
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How does the ionic radius affect lattice enthalpy?
How does the ionic radius affect lattice enthalpy?
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What is the overall change in enthalpy, ΔHf KCl, calculated from the Born-Haber cycle?
What is the overall change in enthalpy, ΔHf KCl, calculated from the Born-Haber cycle?
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Which step in the Born-Haber cycle represents the energy required to form gaseous potassium ions?
Which step in the Born-Haber cycle represents the energy required to form gaseous potassium ions?
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What effect does covalent character have on ionic solids?
What effect does covalent character have on ionic solids?
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In the Born-Haber cycle, how would the change in enthalpy need to be adjusted for a compound like K2O?
In the Born-Haber cycle, how would the change in enthalpy need to be adjusted for a compound like K2O?
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What is the lattice energy represented as in the Born-Haber cycle for KCl?
What is the lattice energy represented as in the Born-Haber cycle for KCl?
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Which reaction represents the formation of the gaseous chlorine atom in the Born-Haber cycle?
Which reaction represents the formation of the gaseous chlorine atom in the Born-Haber cycle?
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Which ΔH value is associated with the electron affinity of chlorine in the cycle?
Which ΔH value is associated with the electron affinity of chlorine in the cycle?
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What is the significance of breaking down ΔHf KCl into its individual components?
What is the significance of breaking down ΔHf KCl into its individual components?
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The perfect ionic model assumes that ions are spherical and electrons are not shared. What does this assumption ignore?
The perfect ionic model assumes that ions are spherical and electrons are not shared. What does this assumption ignore?
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Which of these factors does NOT contribute to the presence of more covalent character in an ionic compound?
Which of these factors does NOT contribute to the presence of more covalent character in an ionic compound?
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How does the covalent character of a ionic solid affect the value of its lattice enthalpy calculated from experimental data?
How does the covalent character of a ionic solid affect the value of its lattice enthalpy calculated from experimental data?
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Which of these ions would have the highest degree of covalent character with a chloride ion?
Which of these ions would have the highest degree of covalent character with a chloride ion?
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Which of the following salts would have the greater covalent character?
Which of the following salts would have the greater covalent character?
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Which of the following statements is TRUE about lattice enthalpy?
Which of the following statements is TRUE about lattice enthalpy?
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Which of the following salts would have the SMALLEST difference between its theoretical lattice enthalpy calculated using the perfect ionic model and its experimental lattice enthalpy determined using a Born-Haber cycle?
Which of the following salts would have the SMALLEST difference between its theoretical lattice enthalpy calculated using the perfect ionic model and its experimental lattice enthalpy determined using a Born-Haber cycle?
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Which of these factors DOES NOT influence the amount of covalent character present in an ionic compound?
Which of these factors DOES NOT influence the amount of covalent character present in an ionic compound?
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Which of the following reactions would have a decrease in entropy?
Which of the following reactions would have a decrease in entropy?
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According to the content provided, what is the relationship between entropy change (ΔS) and the likelihood of a reaction occurring?
According to the content provided, what is the relationship between entropy change (ΔS) and the likelihood of a reaction occurring?
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Which of the following factors does NOT directly contribute to the change in entropy (ΔS) of a reaction?
Which of the following factors does NOT directly contribute to the change in entropy (ΔS) of a reaction?
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What is the entropy change (ΔS) for the reaction: 2SO2(g) + O2(g) → 2SO3(g), given the following standard molar entropies: SO2(g) = 248 J/mol K, O2(g) = 205 J/mol K, and SO3(g) = 256 J/mol K?
What is the entropy change (ΔS) for the reaction: 2SO2(g) + O2(g) → 2SO3(g), given the following standard molar entropies: SO2(g) = 248 J/mol K, O2(g) = 205 J/mol K, and SO3(g) = 256 J/mol K?
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Which of the following reactions would likely have a positive entropy change (ΔS)?
Which of the following reactions would likely have a positive entropy change (ΔS)?
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Why does the formation of a solid from aqueous ions generally have a decrease in entropy?
Why does the formation of a solid from aqueous ions generally have a decrease in entropy?
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What is the primary reason for the decrease in entropy in the reaction N2(g) + 3H2(g) → 2NH3(g)?
What is the primary reason for the decrease in entropy in the reaction N2(g) + 3H2(g) → 2NH3(g)?
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Using the table provided, which of the following changes would likely lead to an increase in entropy?
Using the table provided, which of the following changes would likely lead to an increase in entropy?
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Study Notes
Lattice Enthalpy
- Lattice enthalpy describes the attraction forces between ions in an ionic substance.
- Lattice structure: ions arranged in a regular, alternating pattern.
- Enthalpy of Lattice Dissociation (ΔHLATT DISS): the enthalpy change when 1 mole of an ionic substance dissociates into gaseous ions.
- Example: NaCl(s) → Na+(g) + Cl-(g)
- ΔHLATT DISS is always positive (+ΔH). Energy is required to break attractions between ions.
- Enthalpy of Lattice Association (ΔHLATT ASS): the enthalpy change when 1 mole of an ionic substance is formed from its gaseous ions
- Example: Na+(g) + Cl-(g) → NaCl(s)
- ΔHLATT ASS is always negative (-ΔH). Energy is released when attractions form between ions.
- Important factors influencing lattice enthalpy:
- Ionic charge: greater charge, stronger attraction, and larger lattice enthalpy.
- Ionic radius: smaller radius, stronger attraction, and larger lattice enthalpy.
Hints and Tips
- Enthalpy values for association and dissociation are equal and opposite.
- Stronger attractions between ions result in a larger lattice enthalpy.
- Factors affecting ionic attraction strength and size of lattice enthalpy:
- Charge on the ions: greater charge = stronger attraction
- Ionic radius: smaller radius = stronger attraction
Born-Haber Cycles
- Born-Haber cycles are alternative routes to calculate enthalpy of formation for ionic substances
- They break down the process of creating an ionic compound from its constituent elements into stages.
- Three basic stages for both metal and non-metal:
- Atomisation: elements converted to individual gaseous atoms (ΔHatom).
- Ionisation: metal atoms lose electrons to form positive ions, non-metal atoms gain electrons to form negative ions (ΔHI.E., ΔHE.A).
- Lattice association: gaseous ions combine to form the ionic lattice (ΔHlatt ass).
∆H Definitions
- ∆Hformation: enthalpy change when 1 mole of a compound is formed from its constituent elements in their standard states.
- ∆Hatomisation: enthalpy change when 1 mole of an element is converted into gaseous atoms in standard state
- ∆Hbond enthalpy: average enthalpy change when 1 mole of covalent bonds are broken in gaseous state
- ∆Hionisation energy: enthalpy change per mole of electrons removed from 1 mole gaseous atoms
- ∆Helectron affinity: enthalpy change per mole of electrons added to 1 mole gaseous atoms
- ∆Hlattice association: enthalpy change when 1 mole of an ionic substance is formed from its gaseous ions
Different combinations of ions in Born-Haber Cycles
- Group 1 + group 7
- Group 1 + group 6
- Group 2 + group 7
- Group 2 + group 6
- Must account for number of ions in the formulas during calculations
Enthalpy of Solution (∆Hsol)
- ∆Hsol is the enthalpy change when 1 mole of a solid ionic substance dissolves in water.
- two stage process:
- separation of ions in the lattice(∆Hlatt diss).
- Hydration of the ions (∆Hhyd).
- ∆Hsol = ∆Hlatt diss + ∆Hhyd
- exothermic if ∆Hsol < 0 (negative)
- endothermic if ∆Hsol > 0 (positive)
Entropy (S)
- Entropy: measure of disorder/ randomness in a system
- Units: J K-1 mol-1
- Factors affecting entropy:
- State of matter: gases > liquids > solids/ aqueous
- Number of moles of substance: higher number of moles = higher entropy.
Entropy Change (∆S)
- ∆S is the change in entropy
- Positive ( + ∆S) if entropy increases.
- Negative (- ∆S) if entropy decreases.
- ∆Ssystem = ∑∆Sproducts - ∑∆Sreactants (calculate using entropy data)
Gibbs Free Energy Change (∆G)
- ∆G is used to predict if a reaction can occur spontaneously at a given temperature.
- ∆G = ∆H - T∆S.
- ∆G < 0 (negative): reaction is spontaneous
- ∆G > 0 (positive): reaction is non-spontaneous.
- ∆G = Zero: reaction is at equilibrium.
- The effect of temperature on feasibility depends on ∆H and ∆S values:
Hints & Tips
- Important to note units are consistent.
- Pay attention to how to calculate values including temperature and change in number of moles and also to the sign conventions (T must be positive).
- Remember the enthalpy of lattice association & its relationship to lattice dissociation.
Perfect Ionic Model VS Born-Haber Cycle
-
Theoretical model vs experimental data determines the difference between the model and cycle.
-
Covalent character: Greater difference between theoretical and experimental values indicates more covalent character in the ionic compound.
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Description
Test your understanding of lattice enthalpy with this quiz. Explore key concepts such as lattice dissociation and association, as well as the factors affecting lattice enthalpy. It's perfect for students studying ionic compounds and thermochemistry.
