Question

Which balanced equation represents a redox

reaction?
(1) PCl5 ==> PCl3 + Cl2
(2) KOH + HCl ==> KCl + H=O
(3) LiBr==> Li+ + Br=
(4) Ca2+ + SO42- ==>CaSO4

Answer 1

Answer: (1) PCl5 ==> PCl3 + Cl2

Explanation: PCl5 == PCl3 + Cl2 is a redox reaction. In a redox reaction, there will be a change in oxidation number for two elements. The oxidation number of the P is +5 in Pcl5 and it is +3 in PCl3, so the P is reduced. The Cl has an oxidation number of -1 in PCl5, but as a free elements in Cl2 it has an oxidation number of zero, so it is oxidized. Always look for free elements to help identify redox reactions.