δu = q - w

Definition

The equation δu = q - w represents 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 foundational principle highlights the conservation of energy, emphasizing that energy cannot be created or destroyed, only transformed between heat and work. Understanding this relationship is crucial for analyzing energy transfers in thermodynamic processes.

5 Must Know Facts For Your Next Test

1. The first law of thermodynamics emphasizes that the total energy of an isolated system remains constant, making energy conservation a core principle.
2. In this equation, 'q' can be positive or negative; positive when heat is added to the system and negative when heat is removed.
3. The 'w' term signifies work done by the system on its surroundings, which is considered positive when energy is leaving the system.
4. The relationship illustrates how different forms of energy—internal energy, heat, and work—interact during thermodynamic processes.
5. This equation lays the groundwork for understanding more complex topics like cyclic processes and efficiency in engines.

Review Questions

• How does the equation δu = q - w illustrate the conservation of energy principle in thermodynamics?
  • The equation δu = q - w shows how energy within a system changes based on heat transfer and work done. By stating that the change in internal energy (δu) equals the heat added (q) minus the work done (w), it highlights that all energy entering or leaving a system must balance out. This encapsulates the conservation of energy, as any increase in internal energy results from incoming heat or a decrease due to work performed by the system.
• Discuss the implications of positive and negative values for 'q' and 'w' in relation to internal energy changes.
  • Positive values for 'q' indicate that heat is being added to the system, which increases internal energy. Conversely, negative values for 'q' mean that heat is being removed, decreasing internal energy. For work ('w'), positive values suggest that the system is doing work on its surroundings, resulting in a loss of internal energy. Understanding these signs helps predict how a system's internal energy will change based on heat transfer and work interactions.
• Evaluate how δu = q - w can be applied to real-world scenarios such as engines or refrigerators.
  • Applying δu = q - w to real-world scenarios allows for analyzing energy efficiency in devices like engines and refrigerators. In an engine, fuel combustion adds heat (positive q), while work is done to move parts (positive w), leading to changes in internal energy. Conversely, in a refrigerator, work is done on the refrigerant (positive w), allowing heat to be extracted from inside (negative q), demonstrating how energy is conserved and transferred effectively in practical applications. Evaluating these processes using this equation helps engineers design more efficient systems.

Related terms

Internal Energy: The total energy contained within a system, including kinetic and potential energies at the molecular level.

Heat Transfer: The process by which thermal energy moves from one body or system to another, typically due to a temperature difference.

Work: The energy transferred when a force is applied to move an object, often associated with volume changes in thermodynamic systems.