An extinction event is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms. It occurs when the rate of extinction increases with respect to the rate of speciation. -Wikipedia
About 255.3 grams is the answer I believe. I just had a school work packet and had that question on it, and that is the answer that I had put on it I believe.
Answer: 
kJ
Explanation:
The thermochemical equation for decomposition of ammonium nitrate is:
Given mass= 50.0 kg =
(1kg=1000g)
According to stoichiometry:
1 mole of 
gives = 82.1 kJ of heat
Thus 
of give =
kJ of heat
Thus kJ of heat is evolved from the decomposition of 50.0 kg of ammonium nitrate.
Electrons - they are the particles that determine the chemical properties of an element
