Free energy measures from a QV curve. (A) A hypothetical normalized QV curve. The vertical dashed line is the V = 0 axis. The shaded area is the integral $∫01V dQ−f$ (⁠$Q−f=Q−/Qmax$⁠), which equals $ΔG−C/Qmax.$ The integral is negative on the left of the V = 0 axis and positive on the right, as indicated by the − and + signs. (B) The same QV curve with the median voltage of charge movement (V_m) marked by the vertical dashed lines. The areas on either side of the V_m axis are equal and are both positive. (C) The QV curve intersected by the V = 0 and V = V_m axes. The area of the shaded rectangle is equal to the sum of the two areas shaded in A, taking their respective signs into consideration.