Question

which reaction is exothermic?
○ a reaction that absorbs energy from the environment
○ a reaction that requires an activation energy
○ a reaction that releases energy into the environment
○ a reaction that does not involve a change in energy

Explanation:

To determine the exothermic reaction, recall the definition: an exothermic reaction releases energy (e.g., heat) into the environment. Let's analyze each option:

• "a reaction that absorbs energy from the environment" describes an endothermic reaction, not exothermic.
• "a reaction that requires an activation energy" is true for most reactions (both exo and endo) and does not define exothermicity.
• "a reaction that releases energy into the environment" matches the exothermic definition.
• "a reaction that does not involve a change in energy" is incorrect, as reactions involve energy changes (exo or endo).

Answer:

a reaction that releases energy into the environment