Solution to Example 1
Given:
Total pressure PT = 1.0132 x 105 Pa (constant)
Temperature T = 298 K
DAB = 0.230 x 10-4 m2/s
R = 8314 m3.Pa/kg-mole.K
At point 1, pA1 = 1.013 x 104 Pa
At point 2, pA2 = 0.507 x 104 Pa
Diffusion path = ( z2 - z1 ) = 0.1 m
We can use the following equation for flux of A in a binary mixture with B:
Component-A is diffusing from Point 1 to Point 2, as its partial pressure is higher at point 1.
Putting in the number and check for the appropriate units:
We can use the Dalton's Law of partial pressures to determine the partial pressures
of component-B at points 1 and 2:
PT = pA + pB
At point 1:
pB1 = PT - pA1
PB1 = 1.0132 x 105 - 1.013 x 104 = 91,190 Pa
At point 2:
pB2 = PT - pA2
PB2 = 1.0132 x 105 - 0.507 x 104 = 96,250 Pa
Component-B is diffusing in the opposite direction to component-A: from Point 2 to Point 1, as the partial pressure for B at point 1 is higher.
We can calculate the flux of B in A using: 
Thus: 
The flux for component-B is the same as the flux for component-A, but with a negative sign, indicating that it is in the opposite direction. The 2 components are diffusing in opposite direction. This is the concept of Equimolar Counter-Diffusion.