What is typically observed in a chemical reaction involving energy transfer?

In chemical reactions, energy transfer is a fundamental aspect that can manifest in various ways, primarily through the release or absorption of heat. When a reaction occurs, it can either release energy into the surroundings, known as an exothermic reaction, or absorb energy from the surroundings, referred to as an endothermic reaction.

This energy change is a key characteristic of chemical reactions, as it often influences the phase of the substances involved, the rate of the reaction, and the overall energetics of the system. Heat is commonly the form of energy that is measured in such processes, making it an observable and critical component when studying chemical reactions.

The other options do not accurately represent the behavior of energy in chemical reactions. For instance, stating that a reaction requires external energy only overlooks the processes where energy is released. Saying there is no energy change contradicts the fundamental principles of thermodynamics in chemistry, which state that energy is always conserved, though it may change forms. Lastly, limiting the discussion solely to light energy ignores the significant role that thermal energy plays in many reactions. Thus, the correct answer highlights the dual nature of energy transfer in chemical processes.