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

• A. The energy needed to break bonds is less than the energy released when new bonds are formed.
• B. The energy required to break bonds is more than energy released.
• C. The energy required to break bonds equals energy released.
• D. There is no bond breaking.

Answer: (A)

Exothermic behavior comes from the balance of energy in breaking old bonds and forming new ones. Breaking bonds requires energy input, while forming new bonds releases energy. If the energy released when new bonds form is greater than the energy needed to break the old bonds, the extra energy leaves as heat to the surroundings. That net release of heat is what defines an exothermic reaction. So the condition is: energy to break bonds is less than energy released when new bonds form.

That’s why the other scenarios don’t fit: if breaking bonds costs more energy than is released, the system absorbs heat (endothermic). If they’re equal, there’s no net heat change. If there’s no bond breaking, there isn’t the energy balance that leads to heat release in a typical reaction.