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Questions and Answers
Why do gases generally have greater entropy compared to solids and liquids?
Why do gases generally have greater entropy compared to solids and liquids?
What does entropy measure in chemistry?
What does entropy measure in chemistry?
What happens to entropy as temperature increases?
What happens to entropy as temperature increases?
What change in entropy occurs when a substance melts or evaporates?
What change in entropy occurs when a substance melts or evaporates?
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What kind of entropy value do spontaneous reactions possess?
What kind of entropy value do spontaneous reactions possess?
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How does Gibbs Free-Energy help determine entropy without measuring effects on surroundings?
How does Gibbs Free-Energy help determine entropy without measuring effects on surroundings?
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What is lattice dissociation enthalpy?
What is lattice dissociation enthalpy?
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What is the definition of atomisation enthalpy?
What is the definition of atomisation enthalpy?
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What does the enthalpy of electron affinity measure?
What does the enthalpy of electron affinity measure?
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What type of substances are lattice enthalpies used for?
What type of substances are lattice enthalpies used for?
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How are Born-Haber cycles related to Hess's Law?
How are Born-Haber cycles related to Hess's Law?
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Which term describes the energy required to form an ionic lattice from its constituent ions?
Which term describes the energy required to form an ionic lattice from its constituent ions?
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What happens to the sign of the enthalpy change if the cycle counters the direction of the arrow?
What happens to the sign of the enthalpy change if the cycle counters the direction of the arrow?
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How is enthalpy of solution defined?
How is enthalpy of solution defined?
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What is enthalpy of hydration defined as?
What is enthalpy of hydration defined as?
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Why is enthalpy of hydration nearly always negative?
Why is enthalpy of hydration nearly always negative?
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In the perfect ionic model, what assumption is made about the ions?
In the perfect ionic model, what assumption is made about the ions?
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How are enthalpies of solution and hydration combined to form an energy cycle?
How are enthalpies of solution and hydration combined to form an energy cycle?
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Study Notes
Entropy and Thermodynamics
- Gases generally have greater entropy compared to solids and liquids due to the higher disorder and randomness of their molecular arrangements.
- Entropy measures the disorder or randomness of a system in chemistry, typically denoted as 'S' and measured in units of J/K.
- As temperature increases, entropy also increases, indicating a greater degree of disorder or randomness in the system.
- When a substance melts or evaporates, its entropy increases due to the increased disorder of its molecular arrangement.
Thermodynamic Properties
- Spontaneous reactions possess a negative entropy change, indicating an increase in disorder or randomness.
- Gibbs Free-Energy (ΔG) helps determine entropy without measuring effects on surroundings by considering the energy available to do work.
Enthalpy and Lattice Energy
- Lattice dissociation enthalpy is the energy required to separate one mole of an ionic solid into its constituent gaseous ions.
- Atomisation enthalpy is the energy required to completely break down a mole of a substance into its individual atoms.
- Enthalpy of electron affinity measures the energy change when an electron is added to an atom or molecule.
- Lattice enthalpies are used for ionic substances, which involve the energy required to form an ionic lattice from its constituent ions.
Thermochemical Cycles
- Born-Haber cycles are related to Hess's Law, which states that the total enthalpy change in a reaction is equal to the sum of the enthalpy changes of the individual steps.
- The energy required to form an ionic lattice from its constituent ions is described by the lattice enthalpy.
- If the cycle counters the direction of the arrow, the sign of the enthalpy change is reversed.
Enthalpy of Solution and Hydration
- Enthalpy of solution is the energy change when one mole of a substance dissolves in a solvent.
- Enthalpy of hydration is the energy change when a mole of a substance is surrounded by water molecules, typically resulting in a negative value due to the stabilization of the solute.
- Enthalpies of solution and hydration are combined to form an energy cycle, allowing the calculation of lattice enthalpies.
Ionic Model Assumptions
- In the perfect ionic model, it is assumed that the ions interact only through electrostatic forces, ignoring any covalent character or van der Waals forces.
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Description
Explore detailed notes on Born-Haber cycles in AQA Chemistry A-level 3.1.8, which are essential for determining enthalpy changes in ionic substances. Learn how to use Born-Haber cycles similar to Hess's Law cycles to calculate lattice enthalpies.
