Question

What is half equation?

Answer 1

Half-equations:

A half-equation shows us what happens at one of the electrodes during electrolysis. We should complete and balance half-equations for the reactions that happen during electrolysis.

Writing a half-equation:

Electrons are shown as e in half-equations. A half-equation is balanced by adding, or taking away, a number of electrons equal to the total number of charges on the ions in the equation.

For example, here is how you would write the balanced half-equation for chloride ions forming chlorine gas:

Step Result

1. Write the formulae of the reactant and product.
$C{l}^{-}\to C_{12}$
2. Adjust the number of ions, if needed.
$2C{l}^{-}\to C_{12}$
3. Count the number of charges. Add enough electrons so that both sides have the same total number of charges.
$2C{l}^{-}\to C_{12}2e^{-}$
This half - equation written as:
$2C{l}^{-}-2e^{-}\to C_{12}$

The table shows some examples of half-equations before and after balancing.
Unbalanced Balanced
$A^{13+}+e^{-}\to Al{A}^{13+}+3e^{-}\to AlC{l}^{2+}+e^{-}\to CuC{u}^{2+}+2e^{-}\to Cu{H}^{+}+e^{-}\to H_{2}2H^{+}+2e^{-}\to H_{2}B{r}^{-}\to B{r}_2+2e^{-}{O}^{2-}\to O_2+e^{-}2O_2\to O_2+4e^{-}$