# Dalton's Law

The total pressure of a mixture of gases is made up by the sum of the partial pressures of the components in the mixture - also known from Gibbs'-Dalton's Law of Partial Pressures.

*the total pressure exerted by a mixture of gases is the sum of the partial pressures of the individual gases*

The total pressure in a mixture of gases can be expressed as:

p_{ total }= p_{1}+ p_{2}+ .. + p_{ n }

= Σp_{ i }(1)

where

p_{ total }= total pressure of mixture (Pa, psi)

p_{ i }= partial pressure of individual gas (Pa, psi)

Assuming that each gas behaves ideally - the partial pressure for each gas can calculated from the Ideal gas Law as

* p _{ i } = n_{1} R T / V (2) *

* where *

* p _{ i } = pressure (Pa, psi) *

* n _{1} = the number of moles of the gas *

* R = universal gas constant (J/(mol K), lb _{f} ft/(lb mol ^{ o } R), 8.3145 (J/(mol K)) *

* T = absolute temperature (K, ^{ o } R) *

* V = volume (m ^{3}, ft^{3} ) *

### Example - Partial Pressure of single Gas

If there is * 2 moles * of gas in * 0.005 m ^{3} * volume (

*5 litre*) with temperature

*27°C*(

*300 K*) - the partial pressure of the gas can be calculated as

* p _{ i } = (2) ( 8.3145 J/(mol K) ) (300 K) / (0.005 m^{3} ) *

* = 997740 Pa *

* = 997 kPa *

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