AQA Chemistry A-level - Born-Haber Cycles

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What does the enthalpy of solution represent?

The energy released when one mole of liquid is formed from gas.

The enthalpy change when one mole of ionic solid is dissolved in water to infinite dilution. (correct)

The enthalpy change when one mole of gas is liquefied.

The enthalpy change when one mole of solid is formed from aqueous ions.

Why is the enthalpy of hydration typically negative?

Gaseous ions condense into liquids upon dissolution.

The ions do not interact at all.

All hydration processes require energy to occur.

Water has a partially positive region that attracts negatively charged ions. (correct)

Which assumption is part of the perfect ionic model?

Ions can easily be polarized.

Ions are perfectly spherical. (correct)

Ions have varying sizes and charge distributions.

Ions exhibit significant covalent character.

How does the entropy of a substance change as temperature increases?

It increases because particles gain energy and move apart. Signup and view all the answers

What is the relationship between spontaneous reactions and entropy?

Spontaneous reactions are characterized by a positive entropy change. Signup and view all the answers

Which option correctly describes the entropy change during vaporization compared to fusion?

Entropy change during vaporization is more than during fusion. Signup and view all the answers

What does Gibbs Free-Energy (∆G) allow researchers to do?

Calculate entropy without measuring changes in surroundings. Signup and view all the answers

In which state do substances exhibit the greatest entropy?

Gases. Signup and view all the answers

What is the definition of lattice dissociation enthalpy?

The energy required to break apart an ionic lattice into gaseous ions. Signup and view all the answers

Which term describes the energy needed to form a mole of gaseous atoms?

Enthalpy of atomisation Signup and view all the answers

How are enthalpy changes represented in a Born-Haber cycle?

As vectors where the direction determines the sign of the enthalpy change Signup and view all the answers

What do lattice formation enthalpy and lattice dissociation enthalpy measure?

Both reflect the energy involved in the transition of ionic species to and from the gaseous state. Signup and view all the answers

What role do the enthalpy of solution and enthalpy of hydration play in thermodynamics?

They measure lattice enthalpies indirectly. Signup and view all the answers

In a Born-Haber cycle, what occurs if the cycle counters the direction of the enthalpy change arrow?

The sign of the enthalpy change is reversed. Signup and view all the answers

Which of the following does not directly involve gaseous ions?

Enthalpy of hydration Signup and view all the answers

What is the common feature of lattice enthalpies, atomisation enthalpy, and enthalpy of electron affinity?

Each defines energy changes at standard conditions. Signup and view all the answers

Study Notes

AQA Chemistry A-level - Thermodynamics

3.1.8.1 Born-Haber Cycles

Born-Haber cycles are similar to Hess's Law cycles, allowing calculation of enthalpy changes that can't be measured directly.
Lattice Enthalpies (ΔH): Used for ionic substances, these represent the energy required to break an ionic lattice into gaseous ions.
Lattice dissociation enthalpy: The energy needed to separate an ionic lattice into its gaseous ions.
Lattice formation enthalpy: The energy required to form an ionic lattice from its gaseous ions.
Atomisation Enthalpy (ΔatH): The energy needed to form one mole of gaseous atoms from the element in its standard state.
Enthalpy of Electron Affinity (ΔH): The enthalpy change when one mole of electrons is added to a mole of gaseous atoms.

Born-Haber Cycle Example

The example shows calculating enthalpy of formation (ΔHf°) of NaCl(s), calculating the enthalpy change by following the arrows until the desired state.
If the cycle reverses the direction of the arrow, reverse the sign of the enthalpy change.

Enthalpies of Solution and Hydration

Enthalpies of Solution (ΔsolH): The enthalpy change when one mole of an ionic solid dissolves in water to infinite dilution.
Enthalpies of Hydration (ΔhydH): The enthalpy change when one mole of gaseous ions dissolves in water to form one mole of aqueous ions.

Perfect Ionic Model

The perfect ionic model assumes ions are perfectly spherical and show no covalent character.
Hydration enthalpy is affected by the size and charge of the ions. Covalent character occurs if the ions have varying sizes or charges leading to unequal distributions of charges.

3.1.8.2 Gibbs Free-Energy and Entropy

Entropy (ΔS): A measure of disorder; increasing temperature leads to more disorder.
Entropy increases from solids (ordered) to liquids (less ordered) to gases (disordered).
The entropy of vaporisation exceeds the entropy of fusion because gaseous state is more disordered than liquid.
Gibbs Free Energy (ΔG): ΔG = ΔH - TΔS (at constant temperature and pressure), this measures if a reaction or process will occur spontaneously.
Negative ΔG indicates spontaneous reactions.
A graph of ΔG against temperature will be a straight line with a negative gradient for spontaneous reactions.
If ΔH and ΔS are both positive or negative, a reaction feasibility depends on the temperature.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz focuses on the Born-Haber cycles within the AQA Chemistry A-level curriculum. It covers key concepts such as lattice enthalpies, atomisation enthalpy, and the enthalpy of electron affinity, providing important insights into the enthalpy changes in ionic compounds. Test your understanding by applying these concepts to example problems.