Enthalpy, Entropy, and Gibbs Free Energy Practice Flashcards

A set of vocabulary-based flashcards covering chemical energetics, lattice enthalpy, Born-Haber cycles, solubility, entropy, Gibbs free energy, and equilibrium constants based on lecture notes.

$\Delta_{ea}H$ (First Electron Affinity)

The enthalpy change when $1\,mole$ of gaseous $1-$ ions are made from $1\,mole$ of gaseous atoms, represented as $O(g) + e^- \rightarrow O^-(g)$.

$\Delta_{lattice}H$ (Lattice Enthalpy Change of Formation)

The enthalpy change when $1\,mole$ of a solid ionic compound is formed from its gaseous ions under standard conditions, such as $Ca^{2+}(g) + 2Cl^-(g) \rightarrow CaCl_2(s)$.

$\Delta_{at}H$ (Enthalpy Change of Atomisation)

The enthalpy change when $1\,mole$ of gaseous atoms is made from an element in its standard state, for example $\frac{1}{2}F_2(g) \rightarrow F(g)$.

Born-Haber Cycle Directions

On a cycle diagram, a downward arrow represents an exothermic process, while an upward arrow represents an endothermic process.

Perfect Ionic Model

A theoretical model used to calculate lattice enthalpies assuming ions are perfectly spherical and the charge is evenly distributed within that sphere.

Covalent Characteristics

Properties identified when an experimental lattice enthalpy differs from the theoretical value, indicating the compound does not follow a perfectly ionic model due to polarisation.

Polarisability

The tendency of large anions with a large charge to have their electrons pulled toward a cation; it increases with anion size and charge due to electron repulsion and distance from the nucleus.

Cation Charge Density

The concentration of charge in a small area; smaller cations have a higher charge density and pull electrons toward themselves more readily.

$\Delta_{sol}H$ (Enthalpy Change of Solution)

The enthalpy change when $1\,mole$ of an ionic substance is dissolved in the minimum amount of solvent to ensure no further enthalpy change is observed upon dilution.

$\Delta_{hyd}H$ (Enthalpy Change of Hydration)

The enthalpy change occurring when gaseous ions dissolve in water to form aqueous ions, such as $K^+(g) + Cl^-(g) \rightarrow K^+(aq) + Cl^-(aq)$.

Entropy ($S$)

A measure of disorder in a system, quantified as the number of ways energy can be shared out between particles.

$\Delta S_{system}$ Calculation

The entropy change of the system found using the formula $\Delta S = S_{\text{products}} - S_{\text{reactants}}$ with units of $J\,K^{-1}\,mol^{-1}$.

$\Delta S_{surroundings}$ Calculation

The entropy change of the surroundings calculated using the formula $\Delta S_{\text{surroundings}} = \frac{-\Delta H}{T}$.

$\Delta S_{total}$ Calculation

The sum of entropy changes in the system and surroundings: $\Delta S_{total} = \Delta S_{system} + \Delta S_{surroundings}$; a positive value indicates the reaction is entropically feasible.

Gibbs Free Energy ($\Delta G$)

A thermodynamic potential used to determine feasibility, calculated as $\Delta G = \Delta H - T\Delta S_{system}$.

Thermodynamic Feasibility

A reaction is theoretically feasible if the Gibbs Free Energy change ($\Delta G$) is negative or zero ($\Delta G \le 0$).

Reaction Kinetic Limitations

Reasons a theoretically feasible reaction ($\Delta G$ is negative) might not be observed, including the activation energy ($E_a$) being too high or the rate of reaction being very slow.

Feasibility Temperature Threshold

The minimum temperature required for a reaction to become just feasible, calculated using $T = \frac{\Delta H}{\Delta S_{system}}$.

$\Delta G$ and Equilibrium Constant ($K$) Relation

The logarithmic relationship between Gibbs Free Energy and the equilibrium constant, expressed as $\Delta G = -RT\ln(K)$, where $R = 8.31\,J\,K^{-1}\,mol^{-1}$.