Nitrogen triiodide, NI 3 (s), is unstable and will spontaneously detonate to form a bright purple cloud

Question:

Nitrogen triiodide, NI₃(s), is unstable and will spontaneously detonate to form a bright purple cloud of nitrogen and iodine gases accompanied with a loud “bang,” which suggests a release of energy. Considering the bonds involved, explain why this reaction is likely to release energy.

2 NI3 :I-N-I: BI N :N=N: + 312 :I-I: