Chapters 18 and 19: Aqueous Ionic Equilibrium and Thermodynamics

Practice vocabulary flashcards based on lecture notes covering buffer solutions, internal energy, enthalpy, entropy trends, and Gibbs free energy.

Strong acids and bases

Substances that never form a buffer solution.

Buffer solution mechanism (added acid)

The added acid is neutralized by the conjugate base or weak base.

Buffer solution mechanism (added base)

The added base is neutralized by the weak acid or the conjugate acid.

Henderson-Hasselbalch equation constraint

This equation can only be used when $x$ as a small approximation is valid; otherwise, an ICE table must be used.

Henderson-Hasselbalch Equation for basic buffer solutions

$$pOH = pK_b + \text{log} \frac{[\text{conjugate acid}]}{[\text{weak base}]}$$

Thermodynamics

A branch of physics/chemistry that studies the relationship between heat ($q$), work ($W$), temperature, and energy.

Heat ($q$)

A type of energy caused by a difference in temperature; the flow of thermal energy from higher temperature to lower temperature (q = mc\text{\Delta t}).

Internal energy ($E$ or $u$)

The sum of all energies of a system or the total energy of a system ($\Delta E = q + w$).

First Law of Thermodynamics (Universe)

$\Delta E_{\text{universe}} = 0$; the total energy change of the universe is the sum of system and surrounding changes ($\Delta E_{\text{univ}} = \Delta E_{\text{system}} + \Delta E_{\text{surr}}$).

Enthalpy ($\Delta H$)

Defined by the equation $\Delta H = \Delta E + P\Delta V$; if volume change is negligible, then $\Delta H \approx \Delta E$.

Enthalpy favorability

$\Delta H < 0$ is considered favorable, while $\Delta H > 0$ is considered unfavorable.

Work ($W$) sign convention

If work is done by the system, it is negative ($-$); if work is done on the system, it is positive ($+$).

Entropy ($S$)

Defined by Boltzmann constant as $S = k \text{ln} W$, where $W$ is the number of energetically equivalent ways a system can exist.

Entropy Units

$$J/\text{mol} \cdot K$$

Entropy Trends: Molar Mass

$S$ increases as the molar mass increases, such as $S^{\circ}_{O_2} > S^{\circ}_{N_2}$.

Entropy Trends: Complexity

$S$ increases as the molecule gets more complex, such as $S^{\circ}_{\text{protein}} > S^{\circ}_{CH_4}$.

Entropy Trends: States of Matter

$S$ increases from solids to liquids to gases ($S^{\circ}_{\text{gas}} > S^{\circ}_{\text{liquid}} > S^{\circ}_{\text{solid}}$).

Second Law of Thermodynamics

The entropy of the universe is expanding/increasing ($\Delta S_{\text{univ}} > 0$ for a spontaneous reaction).

Gibbs Free Energy Equation

$$\Delta G = \Delta H - T\Delta S$$

Spontaneity of a reaction

Determined by $\Delta G$ or $\Delta S_{\text{univ}}$, where $\Delta G < 0$ indicates a spontaneous reaction.

Standard Condition Free Energy vs. Equilibrium

$$\Delta G^{\circ}_{\text{rxn}} = -RT \text{ln} K_{eq}$$

Non-standard condition Free Energy

$$\Delta G_{\text{rxn}} = \Delta G^{\circ}_{\text{rxn}} + RT \text{ln} Q$$

Van't Hoff relationship slope

Determined by the equation $\text{ln} K_{eq} = \frac{-\Delta H_{\text{rxn}}}{R} (\frac{1}{T}) + \frac{\Delta S_{\text{rxn}}}{R}$, where the slope equals $\frac{-\Delta H_{\text{rxn}}}{R}$.

Van't Hoff relationship intercept

Determined by the equation $\text{ln} K_{eq} = \frac{-\Delta H_{\text{rxn}}}{R} (\frac{1}{T}) + \frac{\Delta S_{\text{rxn}}}{R}$, where the intercept equals $\frac{\Delta S_{\text{rxn}}}{R}$.