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 is foundational in understanding how energy is conserved and accounted for in various processes, such as chemical reactions and physical changes.

5 Must Know Facts For Your Next Test

1. The first law of thermodynamics can be mathematically expressed as $$ ext{ΔU} = Q - W$$, where $$ ext{ΔU}$$ 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 applies to both closed systems, where no mass is exchanged with the surroundings, and open systems, where mass and energy can cross system boundaries.
3. Understanding the first law is crucial for analyzing energy balances in various processes, including heating, cooling, and phase changes.
4. In chemical reactions, the first law helps predict how much heat will be absorbed or released during a reaction based on the changes in internal energy.
5. The first law also distinguishes between adiabatic processes, where no heat transfer occurs, and non-adiabatic processes, where heat exchange takes place.

Review Questions

• How does the first law of thermodynamics apply to the conservation of energy in chemical reactions?
  • The first law of thermodynamics emphasizes that during chemical reactions, while bonds may break and form, the total energy within the system remains constant. Energy can be transformed into different forms such as heat or work but cannot be lost. This means that any energy absorbed or released during a reaction must account for changes in internal energy and is crucial for calculating reaction efficiencies and outcomes.
• Discuss how the first law of thermodynamics impacts the analysis of heating and cooling processes in engineering applications.
  • In engineering, understanding the first law of thermodynamics is vital for analyzing heating and cooling processes. For example, when heating a substance, the absorbed heat increases its internal energy, which can then lead to changes in temperature or phase. Conversely, during cooling, energy is removed from the system, impacting its state. Engineers must consider these energy transformations to design efficient thermal systems and ensure desired outcomes.
• Evaluate the implications of adiabatic versus non-adiabatic processes as defined by the first law of thermodynamics in practical applications.
  • Adiabatic processes, which occur without heat exchange with the surroundings, illustrate how rapid changes can result in significant temperature shifts due to work done on or by the system. In contrast, non-adiabatic processes allow heat transfer that can moderate temperature variations. Understanding these differences is crucial for designing reactors or heat exchangers, as they influence efficiency, safety measures, and overall process design in industrial applications.

Related terms

Energy Conservation:

The principle that total energy remains constant in an isolated system, where energy can change forms but the total amount does not change.

Heat Transfer: The movement of thermal energy from one object or system to another due to a temperature difference.

Work:

In thermodynamics, work refers to the energy transferred when a force is applied over a distance, contributing to changes in a system's internal energy.