What is referred to as the difference in concentration of a substance from one location to another?

The term that describes the difference in concentration of a substance from one location to another is a concentration gradient. This concept is fundamental in various biological and physical processes, such as diffusion and osmosis, where substances move from areas of higher concentration to areas of lower concentration.

In essence, a concentration gradient is present whenever there is a disparity in how much of a substance exists in two different areas. The steeper the gradient (greater difference in concentration), the more rapid the movement of particles from the high concentration area to the low concentration area. This principle is crucial not only in physiology, such as the movement of oxygen and carbon dioxide across cell membranes, but also in various applications in environmental science, chemistry, and even in sports science when considering gas exchange within the body during physical activities.

The other terms do not adequately capture the concept of concentration differences in location. Concentration equilibrium refers to a state where the concentrations are equal, thus there is no gradient. Concentration balance might imply an equal distribution, which again doesn't represent the change in concentration between two areas. Concentration ratio typically involves comparing two concentrations but doesn't directly refer to the difference in concentration from one location to another.