Question
What happens when
(i) PCl5 is heated?
(ii) H3PO3 is heated?
Write the reactions involved ?
Solution
(i) All the bonds that are present in PCl5 no similar. It has three equatorial and two axial bond, the equatorial bonds are stronger than axial one, therefore when PCl5 is heated strongly.
It decomposes to form: PCl5 
PCl3 + Cl2
(ii) H3PO3, on heating, undergoes disproportionation reaction to form PH3 and H3PO4. The oxidation numbers of P in H3PO3, PH3, and H3PO4 are +3, −3, and +5 respectively. As the oxidation number of the same element is decreasing and increasing during a particular reaction, the reaction is a disproportionation reaction.
