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Scientific Laws & Principles

Landmark laws of chemistry and physics — conservation, gas laws, electrolysis, diffusion, cooling and more

Law of Conservation of Mass

NEWBasic
∑mreactants=∑mproducts\sum m_{\text{reactants}} = \sum m_{\text{products}}

In a closed system, matter is neither created nor destroyed — the total mass before a reaction equals the total mass after.

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Law of Definite Proportions

NEWBasic
mAmB=constant\frac{m_A}{m_B} = \text{constant}

A given chemical compound always contains its component elements in the same fixed ratio by mass, regardless of source.

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Law of Multiple Proportions

NEWIntermediate
m1m2=small integerssmall integers\frac{m_1}{m_2} = \frac{\text{small integers}}{\text{small integers}}

When two elements form more than one compound, the masses of one element combining with a fixed mass of the other are in ratios of small whole numbers.

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Dalton's Law of Partial Pressures

NEWIntermediate
Ptotal=P1+P2+⋯+PnP_{\text{total}} = P_1 + P_2 + \cdots + P_n

The total pressure of a mixture of non-reacting gases equals the sum of the partial pressures each gas would exert alone.

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Graham's Law of Effusion

NEWIntermediate
r1r2=M2M1\frac{r_1}{r_2} = \sqrt{\frac{M_2}{M_1}}

The rate at which a gas effuses through a tiny hole is inversely proportional to the square root of its molar mass.

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Avogadro's Law

NEWBasic
V1n1=V2n2\frac{V_1}{n_1} = \frac{V_2}{n_2}

At the same temperature and pressure, equal volumes of gases contain equal numbers of molecules — so volume is proportional to moles.

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Raoult's Law

NEWAdvanced
Psoln=xsolvent Psolvent∘P_{\text{soln}} = x_{\text{solvent}} \, P^{\circ}_{\text{solvent}}

The vapour pressure of a solvent above a solution equals its mole fraction times the pure solvent's vapour pressure.

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Henry's Law

NEWIntermediate
C=kH PC = k_H \, P

The concentration of a gas dissolved in a liquid is directly proportional to the partial pressure of that gas above the liquid.

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Le Chatelier's Principle

NEWIntermediate
Q<K⇒shift forward,Q>K⇒shift reverseQ < K \Rightarrow \text{shift forward}, \quad Q > K \Rightarrow \text{shift reverse}

When a system at equilibrium is disturbed by a change in concentration, temperature or pressure, it shifts to partially counteract the change.

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Faraday's Laws of Electrolysis

NEWAdvanced
m=Q Mn F=I t Mn Fm = \frac{Q \, M}{n \, F} = \frac{I \, t \, M}{n \, F}

The mass of substance deposited or dissolved at an electrode is proportional to the electric charge passed through the cell.

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Newton's Law of Cooling

NEWIntermediate
T(t)=Ts+(T0−Ts) e−ktT(t) = T_s + (T_0 - T_s)\, e^{-kt}

The rate at which an object cools is proportional to the temperature difference between the object and its surroundings.

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Fick's First Law of Diffusion

NEWAdvanced
J=−DdCdxJ = -D \frac{dC}{dx}

The diffusion flux of particles flows from regions of high concentration to low, proportional to the concentration gradient.

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Bragg's Law

NEWAdvanced
nλ=2dsin⁡θn\lambda = 2d \sin\theta

X-rays reflected from parallel crystal planes interfere constructively when the path difference is a whole number of wavelengths.

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Curie's Law

NEWAdvanced
M=CBTM = C \frac{B}{T}

The magnetization of a paramagnetic material is proportional to the applied magnetic field and inversely proportional to absolute temperature.

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Biot–Savart Law

NEWAdvanced
dB=μ04πI dlsin⁡θr2dB = \frac{\mu_0}{4\pi} \frac{I \, dl \sin\theta}{r^2}

Gives the magnetic field produced at a point by a small element of current-carrying wire.

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Joule's Heating Law

NEWIntermediate
Q=I2RtQ = I^2 R t

The heat generated by an electric current in a conductor is proportional to the square of the current, the resistance and the time.

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Torricelli's Law

NEWIntermediate
v=2ghv = \sqrt{2gh}

The speed of fluid flowing out of an opening equals the speed it would reach falling freely from the height of the fluid surface.

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Wiedemann–Franz Law

NEWAdvanced
κσ=L T\frac{\kappa}{\sigma} = L \, T

For metals, the ratio of thermal conductivity to electrical conductivity is proportional to absolute temperature, with a nearly universal constant.

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