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Chemistry

Reactions, solutions, gases and thermodynamics

Ideal Gas Law

Intermediate
PV=nRTPV = nRT

Relates pressure, volume, moles and temperature of a gas.

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Molarity

Basic
M=nVM = \frac{n}{V}

Concentration in moles of solute per litre of solution.

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Moles from Mass

Basic
n=mMn = \frac{m}{M}

Number of moles from mass and molar mass.

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pH

Basic
pH=log10[H+]pH = -\log_{10}[H^+]

Acidity from hydrogen-ion concentration.

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pOH

Basic
pOH=log10[OH]pOH = -\log_{10}[OH^-]

Basicity from hydroxide-ion concentration.

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Henderson–Hasselbalch

Advanced
pH=pKa+log[A][HA]pH = pK_a + \log\frac{[A^-]}{[HA]}

pH of a buffer solution.

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Dilution Equation

Basic
C1V1=C2V2C_1 V_1 = C_2 V_2

Relates concentration and volume before and after dilution.

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Rate Law

Intermediate
r=k[A]m[B]nr = k[A]^m[B]^n

Reaction rate as a function of reactant concentrations.

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Arrhenius Equation

Advanced
k=AeEa/RTk = A e^{-E_a/RT}

Temperature dependence of the reaction rate constant.

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Gibbs Free Energy

Advanced
ΔG=ΔHTΔS\Delta G = \Delta H - T\Delta S

Predicts spontaneity of a reaction.

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Nernst Equation

Advanced
E=ERTnFlnQE = E^\circ - \frac{RT}{nF}\ln Q

Cell potential under non-standard conditions.

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Beer–Lambert Law

Advanced
A=εlcA = \varepsilon l c

Absorbance of light by a solution.

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Equilibrium Constant

Advanced
K=[C]c[D]d[A]a[B]bK = \frac{[C]^c[D]^d}{[A]^a[B]^b}

Ratio of product to reactant concentrations at equilibrium.

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Combined Gas Law

Intermediate
P1V1T1=P2V2T2\frac{P_1 V_1}{T_1} = \frac{P_2 V_2}{T_2}

Relates two states of a fixed amount of gas.

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Percent Yield

Intermediate
%=actualtheoretical×100\% = \frac{\text{actual}}{\text{theoretical}} \times 100

Efficiency of a chemical reaction.

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Avogadro's Number

Basic
N=n×NAN = n \times N_A

Number of particles from moles.

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Density

Basic
ρ=mV\rho = \frac{m}{V}

Mass per unit volume of a substance.

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Percent Composition

Basic
%=mass of elementmolar mass×100\% = \frac{\text{mass of element}}{\text{molar mass}} \times 100

Mass percentage of an element in a compound.

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Boyle's Law

Intermediate
P1V1=P2V2P_1 V_1 = P_2 V_2

Pressure and volume are inversely related at constant temperature.

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Charles's Law

Intermediate
V1T1=V2T2\frac{V_1}{T_1} = \frac{V_2}{T_2}

Volume is proportional to temperature at constant pressure.

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Ideal Gas Law

Intermediate
PV=nRTPV = nRT

Relates pressure, volume, moles, and temperature of a gas.

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Boyle Law

Basic
P1V1=P2V2P_1 V_1 = P_2 V_2

At constant temperature, pressure and volume are inversely related.

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Charles Law

Basic
V1T1=V2T2\frac{V_1}{T_1} = \frac{V_2}{T_2}

At constant pressure, volume is proportional to temperature.

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Gay-Lussac Law

Basic
P1T1=P2T2\frac{P_1}{T_1} = \frac{P_2}{T_2}

At constant volume, pressure is proportional to temperature.

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Avogadro Number

Basic
NA=6.022×1023N_A = 6.022\times 10^{23}

Number of particles in one mole.

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Number of Particles

Basic
N=n×NAN = n\times N_A

Particles from moles and Avogadro number.

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Gas Density

Advanced
ρ=PMRT\rho = \frac{PM}{RT}

Density of an ideal gas.

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Rate Law

Advanced
rate=k[A]m[B]nrate = k[A]^m[B]^n

Reaction rate as a function of reactant concentrations.

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First-Order Half-Life

Advanced
t1/2=0.693kt_{1/2} = \frac{0.693}{k}

Half-life of a first-order reaction.

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Mass Percent

Basic
%=msolutemsolution×100\% = \frac{m_{solute}}{m_{solution}}\times 100

Concentration as a percentage by mass.

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Molality

Intermediate
b=nsolutemsolventb = \frac{n_{solute}}{m_{solvent}}

Moles of solute per kilogram of solvent.

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Combined Gas Law

Intermediate
P1V1T1=P2V2T2\frac{P_1 V_1}{T_1} = \frac{P_2 V_2}{T_2}

Combines Boyle, Charles, and Gay-Lussac laws.

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Enthalpy Change

Intermediate
ΔH=HproductsHreactants\Delta H = H_{products} - H_{reactants}

Heat absorbed or released at constant pressure.

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Hess Law

Advanced
ΔH=ΔHsteps\Delta H = \sum \Delta H_{steps}

Total enthalpy change is the sum of step changes.

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pH and pOH

Basic
pH+pOH=14pH + pOH = 14

Relationship between acidity and basicity at 25°C.

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Water Ion Product

Advanced
Kw=[H+][OH]=1014K_w = [H^+][OH^-] = 10^{-14}

Self-ionization constant of water at 25°C.

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