Question

`P + Cl_2 -> PCl_3` is what type of reaction?

Answer 1

Both a redox (oxidation-reduction reaction) and a synthesis reaction

Explanation:

This type of reaction, where there is only one product formed from two or more reactants, is called a synthesis reaction (the word synthesis meaning creation or production).

Not only is this a synthesis reaction, but this can also be classified as an oxidation-redcution reaction (commonly shortened to "redox"). An oxidation-reduction reaction is one in which at least one substance is oxidized (they lost electrons to increase their oxidation state) and at least one other substance is reduced (they gained electrons to decrease their oxidation state).

All pure elements, which both reactants in this case are, have an oxidation state of `0`. When the product `"PCl"_3` is formed, the oxidation state [or, although incorrect (but possibly more familiar), "charge"] of `"Cl"` dropped from `0` to `-1`. Since the oxidation state decreased, the chlorine was reduced. Conversely, the oxidation state of phosphorus increased from `0` to `+3`, so `"P"` was oxidized.