First Law of Thermodynamics

Definition

The First Law of Thermodynamics states that energy cannot be created or destroyed, only transformed from one form to another. This principle emphasizes the conservation of energy in all physical and chemical processes, influencing various fundamental concepts including heat, work, and the behavior of systems at the molecular level.

5 Must Know Facts For Your Next Test

1. The First Law can be expressed mathematically as $$ riangle U = Q - W$$, where $$ riangle U$$ is the change in internal energy, $$Q$$ is the heat added to the system, and $$W$$ is the work done by the system.
2. This law lays the groundwork for understanding energy transfers during chemical reactions and phase changes.
3. The law indicates that if a system absorbs heat (Q) and does work (W), its internal energy (U) will change accordingly.
4. Applications of the First Law include understanding engines, refrigerators, and any process involving heat transfer and work.
5. The First Law reinforces the concept that while energy can change form, such as from thermal to mechanical energy, the total energy in an isolated system remains constant.

Review Questions

• How does the First Law of Thermodynamics relate to the concepts of heat and work in a thermodynamic process?
  • The First Law of Thermodynamics establishes that energy changes within a system are due to heat transfer and work done. When heat is absorbed by a system, it increases internal energy, while doing work on the surroundings decreases that internal energy. The interplay between heat (Q) added to or removed from a system and work (W) performed provides a clear framework for analyzing energy transformations in physical and chemical processes.
• In what ways does the First Law of Thermodynamics support calculations involving internal energy and enthalpy during chemical reactions?
  • The First Law allows for the calculation of changes in internal energy (U) by relating it directly to heat exchanged and work done. In chemical reactions, this translates into determining enthalpy changes, which incorporate both internal energy and pressure-volume work. By understanding these relationships, chemists can predict reaction behavior under varying conditions, making this law essential for thermodynamic calculations.
• Evaluate how the First Law of Thermodynamics is applied in practical scenarios like engines or refrigerators, considering efficiency and energy conversion.
  • The First Law is crucial for assessing how engines convert fuel into mechanical work while maintaining energy conservation principles. For example, in a car engine, chemical energy from fuel transforms into kinetic energy for movement. Similarly, refrigerators use electrical energy to transfer heat against its natural flow. Evaluating efficiency involves understanding how effectively these systems convert one form of energy into another while adhering to the First Law's constraints on total energy within a closed system.

Related terms

Conservation of Energy:

A fundamental principle stating that the total energy of an isolated system remains constant over time, though it can change forms.

Internal Energy:

The total energy contained within a system due to the kinetic and potential energy of its molecules.

Enthalpy:

A thermodynamic quantity equivalent to the total heat content of a system, reflecting both internal energy and the product of pressure and volume.