Final answer:
The first law of thermodynamics states that energy within an isolated system is conserved, and it relates heat transfer, work done, and internal energy. The extension of this law includes the concept of entropy, recognizing that heat transfer cannot be completely reversed, aligning with the second law of thermodynamics.
Step-by-step explanation:
Extension of the Classical First Law of Thermodynamics
The first law of thermodynamics is a reformulation of the law of conservation of energy tailored for thermodynamic systems. It establishes the principle that energy cannot be created or destroyed in an isolated system. The law quantifies the relationship between heat transfer, work done, and the change in internal energy of a system. The law is mathematically represented by the equation ΔU = Q - W, where ΔU represents the change in internal energy of a system, Q is the net heat transfer into the system, and W is the work done by the system.
The extension of this classical law incorporates the realization that not all energy transfer is equal in terms of quality. For example, it explains how work can be fully converted into heat, but the reverse is not entirely possible; some energy is always 'lost' as dissipated heat. This is in accordance with the second law of thermodynamics, which states that heat naturally flows from a hotter to a cooler body. In essence, the extension of the first law integrates the concept of entropy and irreversible processes, leading to a more comprehensive understanding of energy transformations in a system.
Key examples used to illustrate the first law of thermodynamics are processes shown in P-V diagrams, such as the isochoric, isothermal, isobaric, and adiabatic processes. These examples demonstrate how the internal energy changes without involving calculations of heat or internal energy from temperature changes. According to C. P. Snow's humorous statement, the first law's message could be paraphrased as "you can't win," highlighting that one can't obtain more energy from a system than what is put into it.