 No Brain Too Small  CHEMISTRY  Bonding, Structure, Properties & Energy 91164
Information
Oh no! During a thunderstorm lightning strikes
the Auckland Sky Tower.
Q: The energy level diagram shows that this
reaction is endothermic. Explain how.

the energy of reactants.
In lightning the temperature can reach 30,000 °C.
This causes nitrogen and oxygen in the air to react,
producing nitrogen monoxide. This reaction has a
high activation energy and is endothermic.
The energy of product is greater than

Energy / heat is taken in / gained.
 Δ H is positive.
Q: What is meant by the term activation energy?
 Minimum energy needed to start the
reaction / overcome the energy barrier
 Minimum energy needed for a collision to
be successful
The equation that represents this reaction is:
N2(g) + O2(g) 2NO(g)
Energy level diagram for the reaction.
Q: The equation showing the structural formulae
of the reactants and products is
N≡N + O=O  2 N=O
Use the bond energies in the table to calculate
the energy change for this reaction.
Reaction pathway
Bond
Bond energy in kJ
N≡N
945
O=O
498
N=O
630
bonds broken = 945 + 498 = 1443 kJ

bonds made = 2 × -630 = -1260 kJ

energy change = 1443 + -1260
= +183 kJ
Q: Mark in the reactants, product, Ea, and H
Bond energies


Ea
reactants
Q: In terms of bond energies, explain why this
reaction is endothermic.
is less than energy needed to break
+H
existing bonds.
product

Reaction pathway
The energy released forming new bonds
The energy change (ΔH) is + / positive
 No Brain Too Small  CHEMISTRY  Bonding, Structure, Properties & Energy 91164