Question

How can you predict whether it will be thermodynamically favorable for an uncharged substance to move from one side of a membrane to the other?

Short answer

The movement of a substance from one side of the membrane to the other depends on the concentration gradient. The concentration gradient determines the chemical potential difference, which helps decide whether the substance's movement is thermodynamically favorable or not.

Step-by-step solution

Concentration gradient

A concentration gradient arises when particle concentrations are higher in one location than in another. Particles diffuse down a concentration gradient, from higher to lower concentration locations, until they are uniformly distributed in passive transport.

Chemical potential difference

Because the free energy change for transporting a substance across a membrane depends on the concentrations on both sides of the membrane, one can predict whether it will be thermodynamically favorable for an uncharged substance to move from one side of the membrane to the other by checking the concentration gradient.

When the concentrations of a substance on two sides of a membrane differ, a chemical potentialdifference occurs.

Substance movement from one side to the other depends on chemical potential difference

The chemical potential difference can be calculated by using the equation:

$△{\mathrm{G}}_{\mathrm{A}}={\mathrm{G}}_{\mathrm{A}\left(\mathrm{in}\right)}-{\mathrm{G}}_{\mathrm{A}\left(\mathrm{out}\right)}=\mathrm{RT}\left(\frac{{\left[\mathrm{A}\right]}_{\mathrm{in}}}{{\left[\mathrm{A}\right]}_{\mathrm{out}}}\right)$

Where,

[A]=Solute particle.

G_A= Chemical potential

If the concentration [A] outside the membrane is larger than the concentration [A] inside the membrane, the G_A for transport from the outside to the inside will be negative, and A will flow freely inside the membrane. However, if the concentration of [A] inside is higher than outside, then the G_A is positive, and the net flow of A can only occur if it is coupled to an exergonic activity.