In a chemical reaction, it is endothermic if which condition applies?

• A. The energy needed to break bonds is more than the energy released when new bonds are formed.
• B. The energy to break bonds is less than energy released.
• C. The energy to break bonds equals energy released.
• D. The reaction does not involve bond breaking.

Answer: (A)

Endothermic reactions absorb heat because breaking bonds in the reactants requires more energy than is released when new bonds form in the products. When the energy needed to break bonds is greater than the energy released during bond formation, the extra energy must come from the surroundings, so the overall enthalpy change is positive and heat flows into the system. This exactly describes the situation where the energy to break bonds is greater than the energy released.

If the energy to break bonds were less than the energy released, more energy would be released than absorbed, making the process exothermic. If they were equal, there would be no net heat change, i.e., a thermally neutral process. The option stating no bond breaking is involved isn’t a general marker of endothermy, since endothermicity is about net energy absorption, not the mere absence of bond breaking.