Consider a non-reactive binary mixture of two ideal gases A and B in an isothermal horizontal closed tube. Due to the concentration difference at the two ends of the tube, equimolal counterdiffusion occurs along the axial direction. No concentration gradients exist in the radial direction. The profile for partial pressure of component A (pA) as a function of axial distance z is shown in the figure. The partial pressure of component B (pB) approaches zero at z = 0.8 m. At a location z = z1 the partial pressures of the components A and B are equal. The value of z1 (in m) is _____ (rounded off to two decimal places).

Question

Accepted Answer

The correct answer is 0.27 to 0.29. GATE 2026 official key: 0.27 to 0.29. pA rises linearly from ≈0.65 bar at z=0 to ≈2.6 bar at z=0.8 m (total pressure). Setting pA(z1) = P_total/2 = 1.3 bar and solving along the line gives z1 ≈ 0.28 m.