Deduce Feasibility of Redox Reaction

In this JC2 webinar we want to deduce the feasibility of the following redox reaction and state its observations:

feasibility redox reaction question

The reactants are pretty straightforward - Fe3+ and I- ions.

First we need to determine which species undergo oxidation and reduction.

Fe3+ can only be reduced so we will consider the reduction of Fe3+ to Fe2+.

We can find the relevant half equation from the Data Booklet and since Fe3+ is reduced, it should be found on the left hand side of the half equation.

I- can only be oxidised so we will consider the oxidation of I- to I2.

Since I- is oxidised it should be found on the right hand side of the half equation.

feasibility redox reaction choosing half equation

We can now calculate the Ecell for the redox reaction where Fe3+ is reduced and I- is oxidised.

feasibility redox reaction calculate Ecell

Since Ecell is positive, the redox reaction is feasible and we expect the reaction to occur.

We can then write out the observations based on the colours and physical states of the reactants and products.


Fe3+(aq) = yellow solution
I-(aq) = colourless solution

Initial observation = yellow solution


Fe2+(aq) = green solution
I2(aq) = brown solution or I2(s) = black crystals

Final observation = green solution with black crystals or brown solution

feasibility redox reaction deduce feasibility and observation

Topic: Electrochemistry, Physical Chemistry, A Level Chemistry, Singapore

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