AP Chem Big Ideas Summary Cheat Sheet

Key Facts

• The mole relationship is $n = \frac{m}{M}$, where $n$ is moles, $m$ is mass, and $M$ is molar mass.
• For ideal gases, $PV = nRT$, where $P$ is pressure, $V$ is volume, $n$ is moles, $R$ is the gas constant, and $T$ is temperature in kelvins.
• An equilibrium constant is written as $K = \frac{[\text{products}]^{\text{coefficients}}}{[\text{reactants}]^{\text{coefficients}}}$, omitting pure solids and pure liquids.
• For acids and bases, $\mathrm{pH} = -\log[\mathrm{H^+}]$ and $\mathrm{pOH} = -\log[\mathrm{OH^-}]$, with $\mathrm{pH} + \mathrm{pOH} = 14.00$ at $25^\circ\mathrm{C}$.
• The Gibbs free energy relationship is $\Delta G = \Delta H - T\Delta S$, and a process is thermodynamically favorable when $\Delta G < 0$.
• The rate law has the form $\text{rate} = k[A]^m[B]^n$, and the exponents must be determined experimentally rather than from the balanced equation.
• Electrochemical cell potential is related to free energy by $\Delta G^\circ = -nFE^\circ_{\text{cell}}$, so a positive $E^\circ_{\text{cell}}$ gives a negative $\Delta G^\circ$.
• The Nernst equation is $E = E^\circ - \frac{0.0592}{n}\log Q$ at $25^\circ\mathrm{C}$, showing how concentration affects cell voltage.

Vocabulary

Equilibrium

A dynamic state in which the forward and reverse reaction rates are equal and concentrations remain constant.

Enthalpy

The heat energy change of a system at constant pressure, represented by $\Delta H$.

Entropy

A measure of energy dispersal or particle arrangement disorder, represented by $\Delta S$.

Activation Energy

The minimum energy particles must have to react successfully, represented by $E_a$.

Oxidation

The loss of electrons by a substance, which increases its oxidation number.

Buffer

A solution containing a weak acid and its conjugate base, or a weak base and its conjugate acid, that resists changes in $\mathrm{pH}$.