GATE 2026 CH – Question 33
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 ($p_A$) as a function of axial distance $z$ is shown in the figure. The partial pressure of component B ($p_B$) approaches zero at $z = 0.8$ m. At a location $z = z_1$ the partial pressures of the components A and B are equal. The value of $z_1$ (in m) is _____ (rounded off to two decimal places).
Practise this question in The GATE Grind →
Show answer and explanation
Correct answer: 0.27 to 0.29
Explanation
For equimolal counterdiffusion the total pressure is constant, and at $z = 0.8$ m $p_B = 0$, so the total pressure equals $p_A$ there, which is 2.6 bar from the graph. The line for $p_A$ goes from 0.6 bar at $z = 0$ to 2.6 bar at $z = 0.8$ m, a slope of 2.5 bar/m. When $p_A = p_B$, each is half the total, 1.3 bar. Then $z_1 = \frac{1.3 - 0.6}{2.5} = 0.28$ m.