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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