# Would this be a good reducing agent? Given the following standard reduction potential: Cu2+(aq) + e- → Cu+(aq) Eo = 0.15V Fe3+(aq) + e- → Fe2+(aq) Eo = 0.77V

Mar 14, 2016

${\text{Cu}}^{+}$ will be the reducing agent if the 2 half-cells are connected.

#### Explanation:

Consider the ${\text{E}}^{\circ}$ values:

$\stackrel{\textcolor{b l u e}{\leftarrow}}{\textcolor{w h i t e}{\times \times \times \times \times x}}$

$\text{Cu"^(2+)+erightleftharpoons"Cu"^(+)" ""E"^@=+0.15"V}$

$\text{Fe"^(3+)+erightleftharpoons"Fe"^(2+)" ""E"^@=+0.77"V}$

$\stackrel{\textcolor{red}{\rightarrow}}{\textcolor{w h i t e}{\times \times \times \times \times x}}$
When standard electrode potentials are listed -ve to +ve like this you find the most powerful reducing agents at the top right of the list.

They are good reducers because they have a strong tendency to release electrons.

Similarly, you will find the strongest oxidising agents at the bottom left of the table.

They are good oxidisers because they have a strong tendency to take in electrons.

A useful rule of thumb is that "bottom left will oxidise top right".

Or you can say "top right will reduce bottom left.

When 2 half-cells are connected it is the most +ve half-cell that will take in the electrons.

In this case you can see that the ${\text{Fe"^(3+)"/""Fe}}^{2 +}$ half-cell is the most +ve so this will go left to right as shown.

The ${\text{Cu"^(2+)"/""Cu}}^{+}$ half-cell will therefore be driven right to left.

You can see that ${\text{Cu}}^{+}$ is acting as a reducing agent as it is taking in electrons.

The cell reaction is therefore:

${\text{Fe"^(3+)+"Cu"^+rarr"Fe"^(2+)+"Cu}}^{2 +}$

To get the emf of the cell subtract the least +ve ${\text{E}}^{\circ}$ value from the most +ve:

$\text{E"_(cell)=0.77-0.15=+0.62"V}$

If you are familiar with the concept of free energy then:

$\Delta {\text{G"^@=-"nFE}}_{c e l l}^{\circ}$

For a reaction to be feasible the value of $\Delta \text{G}$ must be -ve, so this means a +ve "E_(cell) would indicate that the reaction will happen as written, under standard conditions.