College Physics III – Thermodynamics, Electricity, and Magnetism
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 work (W) done on the system minus the heat (Q) transferred to the system. This fundamental relationship describes the conservation of energy and the interconversion between different forms of energy.
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The First Law of Thermodynamics is a fundamental principle that describes the conservation of energy in a system.
The change in internal energy (ΔU) is the difference between the final and initial internal energies of a system.
Work (W) is the energy transferred to or from a system due to the movement of its boundaries under the action of an external force.
Heat (Q) is the energy transferred to or from a system due to a temperature difference, without the involvement of work.
The First Law of Thermodynamics is often expressed as the statement that energy can be converted from one form to another, but it cannot be created or destroyed.
Review Questions
Explain the physical meaning of the equation ΔU = Q - W and how it relates to the First Law of Thermodynamics.
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 work (W) done on the system minus the heat (Q) transferred to the system. This means that the increase in the internal energy of a system is equal to the net work done on the system plus the net heat transferred to the system. Conversely, the decrease in internal energy is equal to the net work done by the system minus the net heat transferred from the system. This relationship reflects the conservation of energy and the interconversion between different forms of energy.
Analyze the implications of the First Law of Thermodynamics as expressed by the equation ΔU = Q - W.
The First Law of Thermodynamics, as expressed by the equation ΔU = Q - W, has several important implications: 1) It establishes the principle of conservation of energy, stating that energy cannot be created or destroyed, but only converted from one form to another. 2) It shows that the change in a system's internal energy is determined by the net work done on the system and the net heat transferred to the system. 3) It suggests that the internal energy of a system can be increased by doing work on the system or by transferring heat to the system, and can be decreased by doing work with the system or by transferring heat from the system. 4) It provides a framework for understanding and analyzing the energy transformations that occur in various physical and chemical processes.
Evaluate the practical applications of the equation ΔU = Q - W in the context of the First Law of Thermodynamics.
The equation ΔU = Q - W, which represents the First Law of Thermodynamics, has numerous practical applications: 1) It allows for the calculation of the change in internal energy of a system based on the work done on the system and the heat transferred to the system, which is essential for understanding and analyzing the energy transformations in various processes, such as in engines, refrigeration systems, and chemical reactions. 2) It provides a basis for the design and optimization of energy-converting devices, such as heat engines and heat pumps, by enabling the prediction of their efficiency and performance. 3) It is fundamental to the study of thermodynamics and the development of thermodynamic models, which are crucial for understanding and predicting the behavior of systems in fields ranging from engineering to astrophysics. 4) The First Law, as expressed by the equation ΔU = Q - W, is a cornerstone of our understanding of the conservation of energy and the interconversion between different forms of energy, which is essential for the development of sustainable energy technologies and the efficient use of energy resources.