Thermodynamics Flashcards

Interactive active recall cards for Born-Haber cycles, solution enthalpies, entropy, and Gibbs free energy.

Born-Haber Cycles & Lattice Enthalpy: read all 6 questions and answers

Define lattice enthalpy of formation.
The enthalpy change when one mole of a solid ionic compound is formed from its constituent gaseous ions under standard conditions.
Define lattice enthalpy of dissociation.
The enthalpy change when one mole of a solid ionic compound is completely dissociated into its constituent gaseous ions under standard conditions.
What is enthalpy of atomisation?
The enthalpy change when one mole of gaseous atoms is formed from the element in its standard state.
Define first electron affinity.
The enthalpy change when one mole of gaseous 1- ions is formed from one mole of gaseous atoms by gaining one mole of electrons.
Why is the second electron affinity of oxygen endothermic?
Energy is required to overcome the electrostatic repulsion between the negatively charged O^- ion and the incoming negative electron.
What is the difference between experimental and theoretical lattice enthalpies?
Experimental values come from Born-Haber cycles; theoretical values assume a purely ionic model. A difference indicates covalent character in the bonding.

Enthalpies of Solution & Hydration: read all 6 questions and answers

Define enthalpy of hydration.
The enthalpy change when one mole of gaseous ions is dissolved in water to form one mole of aqueous ions under standard conditions.
Define enthalpy of solution.
The enthalpy change when one mole of an ionic solid is completely dissolved in water to form infinitely dilute aqueous ions.
State the equation relating enthalpy of solution, lattice dissociation, and hydration.
Enthalpy of Solution = Lattice Dissociation Enthalpy + Sum of Hydration Enthalpies of all ions.
How does ionic radius affect hydration enthalpy?
A smaller ionic radius results in a higher charge density, attracting water molecules more strongly, making the hydration enthalpy more exothermic.
How does ionic charge affect hydration enthalpy?
A higher ionic charge increases the charge density, attracting polar water molecules more strongly, resulting in a more exothermic hydration enthalpy.
Why can an endothermic enthalpy of solution still lead to a solid dissolving?
If the entropy change (ΔS) is positive and large enough, it can make the overall free energy change (ΔG) negative, rendering dissolution feasible.

Entropy & Gibbs Free Energy: read all 6 questions and answers

Define entropy (S).
A measure of the degree of disorder or randomness in a chemical system.
What are the standard units of entropy?
J K^-1 mol^-1 (Joules per Kelvin per mole).
State the Gibbs free energy equation and its units.
ΔG = ΔH - TΔS, where ΔG is in J mol^-1 (or kJ mol^-1), ΔH is in J mol^-1 (or kJ mol^-1), T is in Kelvin (K), and ΔS is in J K^-1 mol^-1.
Under what condition is a chemical reaction feasible?
A reaction is feasible at a given temperature if the Gibbs free energy change (ΔG) is less than or equal to 0.
State the equation to calculate the temperature at which a reaction becomes feasible.
T = ΔH / ΔS (setting ΔG = 0, and ensuring ΔH and ΔS are in compatible units like Joules).
If ΔH is positive and ΔS is negative, is the reaction ever feasible? Explain.
No, because ΔG will be positive at all temperatures since ΔH is positive and -TΔS will also be positive.