AP Chemistry Formula & Reference Sheet Cheat Sheet

A printable reference covering AP Chemistry constants, equilibrium, thermodynamics, kinetics, gases, electrochemistry, and solution formulas for grades 11-12.

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This AP Chemistry formula and reference sheet gathers the equations, constants, and relationships students use most often on advanced chemistry problems. It is designed to help students choose the right formula quickly, connect variables to units, and avoid searching through notes during review. Students need this cheat sheet because AP Chemistry problems often combine stoichiometry, equilibrium, thermodynamics, kinetics, gases, and electrochemistry in one question.

Key Facts

The ideal gas law is $PV = nRT$ , where $R = 0.08206\ \text{L}\cdot\text{atm}\cdot\text{mol}^{-1}\cdot\text{K}^{-1}$ or $R = 8.314\ \text{J}\cdot\text{mol}^{-1}\cdot\text{K}^{-1}$ depending on units.
Equilibrium constants use concentrations or pressures, with $K_c = \frac{[\text{products}]^{\text{coefficients}}}{[\text{reactants}]^{\text{coefficients}}}$ and $K_p = K_c(RT)^{\Delta n}$ .
Acid and base calculations commonly use $\text{pH} = -\log[\text{H}_3\text{O}^+]$ , $\text{pOH} = -\log[\text{OH}^-]$ , and $\text{pH} + \text{pOH} = 14.00$ at $25^\circ\text{C}$ .
Thermodynamics connects enthalpy, entropy, and free energy with $\Delta G^\circ = \Delta H^\circ - T\Delta S^\circ$ and $\Delta G^\circ = -RT\ln K$ .
Calorimetry uses $q = mc\Delta T$ for temperature change and $q = n\Delta H$ for heat absorbed or released during a chemical process.
Integrated rate laws include zero order $[A]_t = -kt + [A]_0$ , first order $\ln[A]_t = -kt + \ln[A]_0$ , and second order $\frac{1}{[A]_t} = kt + \frac{1}{[A]_0}$ .
Electrochemistry uses $\Delta G^\circ = -nFE^\circ_{\text{cell}}$ and $E_{\text{cell}} = E^\circ_{\text{cell}} - \frac{RT}{nF}\ln Q$ .
Beer-Lambert law relates absorbance to concentration using $A = \varepsilon bc$ , where $\varepsilon$ is molar absorptivity, $b$ is path length, and $c$ is concentration.

Vocabulary

Equilibrium constant: An equilibrium constant is the ratio of product activities to reactant activities at equilibrium, each raised to its stoichiometric coefficient.
Gibbs free energy: Gibbs free energy, $G$ , measures the energy available to do useful work and helps predict whether a process is thermodynamically favored.
Rate law: A rate law is an experimentally determined equation that relates reaction rate to reactant concentrations.
Half-life: Half-life, $t_{1/2}$ , is the time required for the concentration of a reactant to decrease to one-half of its initial value.
Cell potential: Cell potential, $E_{\text{cell}}$ , is the voltage produced by an electrochemical cell due to electron transfer.
Molar absorptivity: Molar absorptivity, $\varepsilon$ , is a constant that describes how strongly a substance absorbs light at a specific wavelength.

Common Mistakes to Avoid

Using the wrong value of $R$ is incorrect because gas law and thermodynamic calculations require consistent units. Use $R = 0.08206\ \text{L}\cdot\text{atm}\cdot\text{mol}^{-1}\cdot\text{K}^{-1}$ with atmospheres and $R = 8.314\ \text{J}\cdot\text{mol}^{-1}\cdot\text{K}^{-1}$ with joules.
Forgetting to convert temperature to kelvin is incorrect because equations such as $PV = nRT$ and $\Delta G^\circ = \Delta H^\circ - T\Delta S^\circ$ require absolute temperature. Convert with $T_K = T_{^\circ\text{C}} + 273.15$ .
Including pure solids or liquids in $K$ expressions is incorrect because their activities are treated as $1$ . Only aqueous species and gases appear in most AP equilibrium expressions.
Mixing signs for heat and work is incorrect because $\Delta E = q + w$ depends on the system’s perspective. Heat absorbed by the system has $q > 0$ , while work done by the system usually has $w < 0$ .
Choosing an integrated rate law without checking graph linearity is incorrect because reaction order must be supported by data. A linear plot of $\ln[A]$ versus $t$ indicates first order, not zero or second order.

Practice Questions

1 A gas sample has $n = 0.750\ \text{mol}$ , $T = 298\ \text{K}$ , and $P = 1.20\ \text{atm}$ . Use $PV = nRT$ to find $V$ in liters.
2 For a reaction at $298\ \text{K}$ , calculate $\Delta G^\circ$ if $K = 4.5 \times 10^3$ using $\Delta G^\circ = -RT\ln K$ .
3 A first-order reaction has $k = 0.035\ \text{s}^{-1}$ and $[A]_0 = 0.80\ \text{M}$ . Use $\ln[A]_t = -kt + \ln[A]_0$ to find $[A]_t$ after $20.0\ \text{s}$ .
4 Explain why a reaction with a large value of $K$ can still be slow at room temperature, even though products are favored at equilibrium.

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