AP Chemistry — Advanced Thermodynamics & Kinetics

Front

Isolated System and Entropy

Back

In an isolated system (no exchange of matter or energy), the total entropy change must be greater than zero ($\Delta S_{total} > 0$) for a spontaneous process. If the system is not isolated, you must account for entropy changes in the surroundings ($\Delta S_{surr} = -\Delta H_{sys}/T$).

Front

Standard Gibbs Free Energy ($\Delta G^\circ$) vs. Reaction Quotient ($Q$)

Back

The relationship is defined as $\Delta G = \Delta G^\circ + RT\ln Q$. At equilibrium, $\Delta G = 0$ and $Q = K$, leading to $\Delta G^\circ = -RT\ln K$. This connects thermodynamics (free energy) to equilibrium constants.

Front

Gibbs-Helmholtz Equation Application

Back

Used to determine how $\Delta G_{rxn}$ changes with temperature when enthalpy ($\Delta H$) and entropy ($\Delta S$) are assumed constant: $\Delta G = \Delta H - T\Delta S$. A reaction becomes spontaneous only when the $T\Delta S$ term overcomes the $\Delta H$ term.

Front

Enthalpy of Solution ($\Delta H_{soln}$) Components

Back

The net enthalpy change is the sum of three steps: $\Delta H_1$ (solute separation, endothermic), $\Delta H_2$ (solvent separation, endothermic), and $\Delta H_3$ (mixing/solvation, exothermic). $\Delta H_{soln} = \Delta H_1 + \Delta H_2 + \Delta H_3$.

Front

Heat ($q$) vs. Work ($w$) Sign Conventions

Back

According to the IUPAC convention used in AP Chemistry: $\Delta U = q + w$. Heat ($q$) is positive if absorbed by the system. Work ($w$) is positive if work is done *on* the system (compression), and negative if work is done *by* the system (expansion: $w = -P\Delta V$).