δu = q - w

Definition

The equation δu = q - w expresses the First Law of Thermodynamics, which states that the change in internal energy (δu) of a system is equal to the heat added to the system (q) minus the work done by the system (w). This principle highlights the conservation of energy, showing how energy can be transferred into or out of a system in the form of heat or work, ultimately affecting the system's internal energy.

5 Must Know Facts For Your Next Test

1. The sign convention is important: heat added to the system is positive, while heat lost is negative; work done by the system is positive, while work done on the system is negative.
2. This equation allows for various forms of energy analysis, whether dealing with isothermal, adiabatic, or other processes in thermodynamics.
3. The First Law of Thermodynamics not only applies to closed systems but can also be extended to open systems with appropriate considerations for mass and energy flow.
4. Understanding this equation is fundamental for solving problems related to energy balances in engines, refrigerators, and other thermal systems.
5. The equation emphasizes that energy cannot be created or destroyed, only transformed from one form to another within a thermodynamic process.

Review Questions

• How does δu = q - w illustrate the principle of energy conservation in thermodynamics?
  • The equation δu = q - w directly reflects the conservation of energy principle by quantifying how energy flows into and out of a system. When heat (q) enters the system, it increases internal energy (δu), while work (w) done by the system reduces internal energy. This balance shows that while energy can change forms between heat and work, the total amount remains constant within a closed system.
• Discuss how different processes like isothermal and adiabatic processes affect the application of δu = q - w.
  • In an isothermal process, temperature remains constant, leading to specific values for q and w that ensure internal energy (δu) stays unchanged since it depends on temperature. Conversely, in an adiabatic process where no heat exchange occurs (q = 0), all work done on or by the system directly results in a change in internal energy (δu = -w). Understanding these distinctions helps in applying the equation effectively across various thermodynamic scenarios.
• Evaluate the implications of δu = q - w for real-world applications such as engines or refrigerators.
  • In real-world applications like engines or refrigerators, δu = q - w is crucial for understanding efficiency and performance. For engines, maximizing work output while minimizing wasted heat reflects a deeper understanding of this relationship. Refrigerators operate by moving heat against its natural flow using work input; thus analyzing their performance through this equation allows for optimizing designs for better energy efficiency. This knowledge is key to developing more sustainable technologies in energy consumption.

Related terms

Internal Energy: The total energy contained within a system due to both its temperature and its molecular structure.

Heat Transfer: The process by which thermal energy moves from a warmer object to a cooler one, typically measured in joules.

Work: In thermodynamics, work refers to energy transfer that occurs when a force is applied over a distance, typically associated with changes in volume against pressure.