Chemistry · Chapter 17

Three Rulers, One Reaction

Cell potential, free energy and the equilibrium constant are three readings of one fact. Drag any ruler and the other two follow. Then change the electron count and watch two rulers stretch while the voltage ruler holds still.

The three rulers the markers never split up

Cell potential, free energy and log K on three rulers that move together

What that K looks like in a beaker

The split between reactant and product at equilibrium

Electrons in the equation

Choose n

Only two of the three rulers care about n. Voltage is energy per unit of charge, so more electrons bring more of both and the ratio holds.

Drag any one of them

+1.10 V
−212 kJ/mol
log K = 37.2
Real cells to drop in

Where this reaction stands

1.5×1037= K spontaneous
Positive voltage
It runs on its own
A positive cell potential gives a negative free energy change, and K lands above one.
ΔG° = −(2)(96485)(1.10) = −212 kJ/mol
log K = (2)(1.10) ÷ 0.0592 = 37.2