In which direction will the redox reaction shown below proceed spontaneously under standard conditions? (Standard reduction potentials: Fe³⁺ 0.77 V, Cr³⁺ -0.41 V)

FeCl₃(aq) + CrCl₂(aq) FeCl₂(aq) + CrCl₃(aq)

The greater the reduction potential of a species, the greater the tendency for that species to be reduced. If, for example, an ion is in the presence of another ion that has a lower reduction potential, then the reduced form of that species will reduce the one with the higher reduction potential. Note that in the example above, Cl anions are spectator ions.

Here we have four ions that ions that form two redox pairs:

Fe³⁺ (oxidized form) and Fe²⁺ (reduced form), and,

Cr³⁺ (oxidized form) and Cr²⁺ (reduced form).

We are given the reduction potentials for

Fe³⁺ + e^- → Fe²⁺ (0.77 V), and for

Cr³⁺ + e^- → Cr²⁺ (-0.41 V).

Fe³⁺ + e^- → Fe²⁺ has a greater reduction potential (0.77 V) than Cr³⁺ + e^- → Cr²⁺ (-0.41 V). This means that Fe³⁺ will be reduced by Cr²⁺, rather than Cr³⁺ being reduced by Fe²⁺. The reaction will proceed from left to right.