δu = q - w

Definition

The equation δu = q - w represents the first law of thermodynamics, indicating 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 fundamental relationship emphasizes the conservation of energy, illustrating how energy can be transferred into or out of a system through heat and work, and how it affects the internal energy of that system.

5 Must Know Facts For Your Next Test

1. The first law of thermodynamics is often summarized as 'energy cannot be created or destroyed, only transformed.'
2. In this equation, 'q' can be positive if heat is added to the system and negative if heat is removed.
3. The work 'w' can be defined as positive when work is done by the system on its surroundings, and negative when work is done on the system.
4. The internal energy change (δu) can also result from changes in temperature, volume, and phase of the system.
5. This equation is foundational for understanding energy balance in closed systems and plays a crucial role in various applications in engineering and natural sciences.

Review Questions

• How does the equation δu = q - w illustrate the concept of energy conservation in thermodynamics?
  • The equation δu = q - w clearly demonstrates energy conservation by stating that any change in a system's internal energy (δu) is directly linked to heat transfer (q) and work done (w). This means that if heat enters the system, it increases internal energy, while if work is done by the system, it decreases internal energy. Therefore, this equation encapsulates how all forms of energy interactions must balance out, adhering to the principle that energy cannot be created or destroyed.
• In what scenarios would you expect the values of 'q' and 'w' to influence the internal energy of a system differently, and why?
  • Scenarios like phase changes highlight how 'q' and 'w' can influence internal energy differently. During a phase change like boiling, heat (q) enters the system without changing temperature but alters internal energy significantly as molecules overcome intermolecular forces. Meanwhile, if work is done on or by the system during this process, it can further affect internal energy. Understanding these dynamics is essential for accurately predicting a system's behavior under different conditions.
• Evaluate how applying δu = q - w in real-world systems helps engineers optimize processes in industries such as power generation.
  • Engineers utilize δu = q - w to analyze and optimize thermal efficiency in power generation systems. By calculating changes in internal energy based on heat input and work output, they can determine areas where energy losses occur and identify potential improvements. For instance, understanding these principles allows for the design of more efficient turbines and heat exchangers that minimize waste while maximizing output. Consequently, applying this thermodynamic principle not only leads to cost savings but also promotes sustainable practices by enhancing overall energy efficiency.

Related terms

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

Heat (q): The form of energy transfer between systems or surroundings due to a temperature difference.

Work (w): The energy transfer that occurs when a force is applied to an object, causing it to move.