What is required in terms of energy to break a chemical bond?
AEnergy is released
BEnergy is absorbed
CNo energy is involved
DEnergy is created
Breaking a chemical bond always requires energy input — you must add energy to pull bonded atoms apart. This is a common point of confusion. It is the reverse process — forming a bond — that releases energy.
Question 2 True / False
In an exothermic reaction, the energy released by forming new bonds is greater than the energy needed to break old bonds.
TTrue
FFalse
Answer: True
An exothermic reaction has a net release of energy because the bond-forming step produces more energy than the bond-breaking step consumes. The surplus energy exits the reaction as heat or light, warming the surroundings.
Question 3 Short Answer
Using the concept of bond energy, explain why burning methane releases heat.
Think about your answer, then reveal below.
Model answer: The energy released by forming the new bonds in the products (CO2 and H2O) is greater than the energy required to break the bonds in the reactants (CH4 and O2), so the excess energy is released as heat.
In the combustion of methane (CH4 + 2O2 → CO2 + 2H2O), the C-H and O=O bonds in the reactants must be broken (energy absorbed), then C=O and O-H bonds form in the products (energy released). The bonds formed in CO2 and H2O are particularly strong, so the energy released during bond formation exceeds the energy consumed during bond breaking, making the overall reaction exothermic.