1 All of the substances listed here are fertilizers that contribute nitrogen to the soil. Which of
these is the richest source of nitrogen on a mass percentage basis?
(a) Urea, (NH2)2CO

answer: enthalpy

explanation:

for a exothermic reaction, the energy is released i.e. the energy of the products is lower than the energy of the reactants.

= enthaply

= energy of products

= energy of reactants

as , thus comes out to be negative. negative value of enthalpy shows that the reaction is exothermic.