The gas hydrazine, N2H4, burns in oxygen like this: N H N H H H (g) + O O (g) N N (g) + 2O H H (g) a Count and list the bonds broken in this reaction. b Count and list the new bonds formed. c Calculate the total energy: i required to break the bonds ii released when the new bonds form. (The bond energies in kJ / mole are: N2H 391; N2N 158; NN 945; O2H 464; O5O 498.)
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
The gas hydrazine, N2H4, burns in oxygen like this:
N
H
N
H
H H
(g) + O O (g) N N (g) + 2O
H
H
(g)
a Count and list the bonds broken in this reaction.
b Count and list the new bonds formed.
c Calculate the total energy:
i required to break the bonds
ii released when the new bonds form.
(The bond energies in kJ / mole are: N2H 391;
N2N 158; NN 945; O2H 464; O5O 498.)
d Calculate the energy change in the reaction.
e Is the reaction exothermic, or endothermic?
f Where is energy transferred from, and to?
g Comment on the suitability of hydrazine as
a fuel.
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