equimolar countercurrent diffusion

Equimolar countercurrent diffusion is a method used to measure the diffusion coefficient of gases. This process involves two gases flowing in opposite directions, with the light molecules moving into the heavy-gas region faster than the heavy molecules move into the light-gas region. This creates a pressure difference that drives the heavy gas into the light-gas region, leading to a steady state where the number of molecules moving in opposite directions is equal.1

This method is sensitive to experimental conditions and is typically carried out in a closed vessel or through a fine capillary or porous material. The diffusion coefficient, denoted as D₁₂, quantifies the rate of diffusion and is inversely proportional to the total pressure or molar density. Diffusion is a slow process, with gaseous diffusion coefficients being significantly faster than those in liquids.1