A hydrogen bond donor is the supplier of the hydrogen atom that is involved in the hydrogen bonding interaction.
A hydrogen bond acceptor is the electronegative atom that 'accepts' the hydrogen in the hydrogen bond. Such electronegative atoms usually possess an unshared pair of electrons such as nitrogen.
We can see from the above definitions that NH3 is able to act in the capacity of a hydrogen bond donor(due to the presence of three N-H bonds) or as a hydrogen bond donor due to presence of an unshared pair on nitrogen atom.
If the reaction is a chemical change, new substances with different properties and identities are formed. This may be indicated by the production of an odor, a change in color or energy, or the formation of a solid.
