What does the first law of thermodynamics state?

The first law of thermodynamics fundamentally emphasizes the principle of conservation of energy. It states that energy cannot be created or destroyed, but can only be transformed from one form to another. This means that the total energy of an isolated system remains constant over time, even as it changes forms—such as from potential energy to kinetic energy or from thermal energy to mechanical energy.

This law is crucial for understanding various physical processes and systems, as it underscores the idea that energy remains constant within a closed system. For instance, when mechanical work is done on a gas, the energy invested into the gas can be observed as an increase in its internal energy, illustrating that while the form of energy may change, the total amount of energy remains unchanged.

The other provided options don't fully capture the essence of the first law. While energy can indeed be transformed and the concept of energy being constant is related, the explicit and accurate assertion of the first law is that energy cannot be created or destroyed. This foundational principle is a cornerstone of both physics and chemistry, playing a significant role in many scientific applications such as thermodynamics, engineering, and environmental science.