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 = p₁ + p₂+ .. + 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 = n₁ R T / V                     (2)

where

p _i = pressure (Pa, psi)

n₁ = 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 (m³, ft³ )

Example - Partial Pressure of single Gas

If there is 2 moles of gas in 0.005 m³ 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 m³ )

= 997740 Pa

= 997 kPa

Temperature ^oC
K
^oF

Length m
km
in
ft
yards
miles
naut miles

Area m²
km²
in²
ft²
miles²
acres

Volume m³
liters
in³
ft³
us gal

Weight kg_f
N
lbf

Velocity m/s
km/h
ft/min
ft/s
mph
knots

Pressure Pa
bar
mm H₂O
kg/cm²
psi
inches H₂O

Flow m³/s
m³/h
US gpm
cfm