What does the first law of thermodynamics state?

The first law of thermodynamics, often referred to as the law of conservation of energy, states that energy cannot be created or destroyed, but it can be transformed from one form to another. This principle underlies many concepts in chemistry and physics, emphasizing that the total energy in a closed system remains constant; it merely changes its form. For example, when chemical energy in a fuel is converted to thermal energy through combustion, the total amount of energy remains unchanged, even though it has converted forms.

This law is fundamental because it implies that in any process—whether chemical reactions, physical changes, or energy transfers—while energy may appear to disappear or be consumed, it is actually just being transformed. This concept is essential for understanding various topics in chemistry, such as stoichiometry, heat transfer, and thermodynamic cycles.