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# Dalton's Law Of Partial Pressures

### Ptotal = Pa + Pb + Pc

vogadro's law (sometimes referred to as Avogadro's hypothesis or Avogadro's principle) is a gas law named after Amedeo Avogadro who, in 1811,  hypothesized that two given samples of an ideal gas, at the same temperature, pressure and volume, contain the same number of molecules.

The pressure of a mixture of gases is equal to the sum of the pressures of all of the constituent gases alone.

Mathematically, this can be represented as:

PressureTotal = Pressure1 + Pressure2 ... Pressuren

Dalton's Law explains that the total pressure is equal to the sum of all of the pressures of the parts. This only is absolutely true for ideal gases, but the error is small for real gases.

Wikipedia - In chemistry and physics, Dalton's law (also called Dalton's law of partial pressures) states that the total pressure exerted by a gaseous mixture is equal to the sum of the partial pressures of each individual component in a gas mixture. This empirical law was observed by John Dalton in 1801 and is related to the ideal gas laws.

Mathematically, the pressure of a mixture of gases can be defined as the summation

$P_{total} = \sum_{i=1} ^ n {p_i}$       or      $P_{total} = p_1 +p_2 + \cdots + p_n$

where $p_{1},\ p_{2},\dots,\ p_{n}$ represent the partial pressure of each component.

It is assumed that the gases do not react with each other.

$\ p_{i} =P_{total}y_i$

where $y_i\ =$ the mole fraction of the i-th component in the total mixture of n components .

The relationship below provides a way to determine the volume based concentration of any individual gaseous component.

$P_i =\frac{P_{total}C_i}{1,000,000}$

where: $C_i\ =$ is the concentration of the ith component expressed in ppm.

Dalton's law is not exactly followed by real gases. Those deviations are considerably large at high pressures. In such conditions, the volume occupied by the molecules can become significant compared to the free space between them. Moreover, the short average distances between molecules raises the intensity of intermolecular forces between gas molecules enough to substantially change the pressure exerted by them. Neither of those effects are considered by the ideal gas model.

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