First Law of Thermodynamics

Definition

The first law of thermodynamics is a fundamental principle that describes the relationship between energy, work, and heat. It states that energy can be transformed from one form to another, but it cannot be created or destroyed; the total energy of an isolated system is constant.

5 Must Know Facts For Your Next Test

1. The first law of thermodynamics states that the change in the internal energy of a system is equal to the sum of the work done on the system and the heat added to the system.
2. The first law of thermodynamics is often expressed mathematically as $\Delta U = Q - W$, where $\Delta U$ is the change in internal energy, $Q$ is the heat added to the system, and $W$ is the work done by the system.
3. The first law of thermodynamics is a fundamental principle that underpins the operation of heat engines, heat pumps, and refrigerators, which are all applications of thermodynamics.
4. The first law of thermodynamics ensures that energy is conserved in a closed system, meaning that energy cannot be created or destroyed, but it can be transformed from one form to another.
5. The first law of thermodynamics is a crucial concept in understanding the efficiency and limitations of energy conversion processes, such as the conversion of thermal energy to mechanical work in a heat engine.

Review Questions

• Explain how the first law of thermodynamics relates to the concepts of thermal energy and work.
  • The first law of thermodynamics describes the relationship between thermal energy, work, and the change in internal energy of a system. It states that the change in internal energy of a system is equal to the sum of the work done on the system and the heat added to the system. This means that energy can be transformed from one form, such as thermal energy, into another form, such as mechanical work, but the total energy of the system remains constant. The first law is fundamental to understanding how energy is converted and conserved in various thermodynamic processes.
• Discuss how the first law of thermodynamics is applied in the context of heat engines, heat pumps, and refrigerators.
  • The first law of thermodynamics is a crucial principle that underpins the operation of heat engines, heat pumps, and refrigerators. In a heat engine, the first law describes how thermal energy is converted into mechanical work, with the efficiency of the process limited by the temperature difference between the hot and cold reservoirs. In a heat pump, the first law explains how work is used to transfer thermal energy from a colder to a warmer reservoir, while in a refrigerator, the first law describes how work is used to transfer thermal energy from a colder to a warmer reservoir, effectively cooling the colder reservoir. The first law provides the fundamental framework for understanding the limitations and performance of these thermodynamic applications.
• Evaluate the significance of the first law of thermodynamics in the context of energy conservation and the limitations of energy conversion processes.
  • The first law of thermodynamics is a profoundly important principle that has far-reaching implications for our understanding of energy and its transformations. By stating that energy can be converted from one form to another but cannot be created or destroyed, the first law establishes the fundamental principle of energy conservation. This has crucial consequences for the design and operation of energy conversion devices, such as heat engines, heat pumps, and refrigerators. The first law also highlights the limitations of these processes, as it demonstrates that there are inherent inefficiencies in converting one form of energy into another. This understanding has driven the development of more efficient energy technologies and has shaped our approach to energy use and conservation, making the first law of thermodynamics a cornerstone of modern physics and engineering.

Related terms

Thermal Energy:

Thermal energy is the internal energy of a substance due to the random motion of its atoms and molecules, and it is directly related to the temperature of the substance.

Work:

Work is the transfer of energy by a force acting through a distance, and it is one of the ways energy can be transformed from one form to another.

Heat Engine:

A heat engine is a device that converts thermal energy into mechanical work, such as an internal combustion engine or a steam turbine.