Final answer:
Energy changes during a chemical reaction as bonds are broken and formed. Energy is absorbed to break bonds and released when new bonds form. The overall energy change depends on whether the reaction is exothermic or endothermic.
Step-by-step explanation:
During a chemical reaction, the energy changes depend on whether bonds are being broken or formed. Energy is absorbed when chemical bonds are broken, as it requires an input of energy to pull apart the atoms. On the other hand, energy is released when new chemical bonds are formed as atoms reach a more stable state. The overall change in energy during a reaction is determined by the balance between these two processes. Reactions can be classified as exothermic or endothermic based on the net energy change.
Conversely, endothermic reactions, such as photosynthesis, absorb more energy during bond breaking than is released in bond formation, thus requiring an additional energy input for the reaction to occur. The concept of free energy is used to quantify the usable energy from a chemical reaction after accounting for energy lost, usually as heat. Despite these energy changes, it's crucial to remember the law of conservation of energy, which states that energy cannot be created or destroyed, only transformed from one form to another.