16.4Electrode and Cell Potentials
Section · module m68823
What this needs
Learn these first — this section will not make sense without them.
log(0.077), a number less than 1, evaluates to a negative logarithm that then gets subtracted (as a double negative) from E°cell — a student who has not internalized that log of a fraction is negative will mishandle the sign and move the potential the wrong direction.
What this touches
Algebra that turns up here. Not a blocker, but this is where you will see it used.
Computing Ecell = Ecathode − Eanode and comparing its sign to predict spontaneity is straightforward subtraction and sign reading, an assumed arithmetic/linear-equation skill the chemistry uses without teaching.
- Applies3.5Composition of Functions
The worked Nernst-equation example first computes Q = [Co²⁺]/[Fe²⁺] = 0.077 from concentrations, then substitutes that number into Ecell = E° − (0.0592/n)log Q — an inner formula's output becomes an outer formula's input, exactly the evaluate-the-inside-function-first pattern §3.5 teaches, and skipping straight to log of the raw concentrations instead of log of Q first is the place this goes wrong.