Question

What would happen if the concentration of h+ ions were the same on both sides of the membrane when the channel opened?

Answer 1

H+ ions would not flow

Answer 2

Diffusion happens against a concentration gradient. Diffusion of a particles occurs when it moves from a region of higher concentration to region on lower concentration. Diffusion occurs as long as there is a difference in concentration. Diffusion stops as soon as there is no concentration gradient.  

There is no diffusion of  H⁺ ions when the channel opens as the concentration of H⁺ ions are the same on both sides of the membrane.