Final answer:
Chemical reactions can be classified as exothermic or endothermic based on whether they release or absorb energy. Energy changes in reactions can be represented by energy-level diagrams. All reactions involve the exchange of energy.
Step-by-step explanation:
Chemical reactions can be classified as exothermic or endothermic based on whether they release or absorb energy, respectively. Exothermic reactions release energy, while endothermic reactions absorb energy. For example, the combustion of methane gas in kitchen burners is an exothermic reaction that releases energy, while photosynthesis is an endothermic reaction that absorbs energy from sunlight.
Energy changes in chemical reactions can be visually represented by energy-level diagrams. In endothermic reactions, the reactants have higher bond energy than the products, indicating that energy is absorbed from the environment. On the other hand, exothermic reactions have higher energy in the reactants than in the products, signifying that energy is released.
It is important to note that all chemical reactions involve the exchange of energy, and the Law of Conservation of Energy states that energy is neither created nor destroyed, but merely changes form.