Internal energy is the total energy contained within a thermodynamic system, including the kinetic energy of the system's particles and the potential energy associated with the configuration of the particles. It represents the sum of all forms of energy present in the system, excluding any energy associated with the system's motion as a whole or with external fields acting on the system.
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The internal energy of a system is the sum of the kinetic energy and potential energy of all the particles within the system.
Changes in a system's internal energy can be caused by the transfer of heat or the performance of work on the system.
The first law of thermodynamics states that the change in a system's internal energy is equal to the sum of the work done on the system and the heat transferred to the system.
The internal energy of a system is a state function, meaning its value depends only on the current state of the system and not on the path taken to reach that state.
The internal energy of a system can be increased by adding heat to the system or by performing work on the system.
Review Questions
Explain how the first law of thermodynamics relates to changes in a system's internal energy.
According to the first law of thermodynamics, the change in a system's internal energy (\$\Delta U\$) is equal to the sum of the work done on the system (\$W\$) and the heat transferred to the system (\$Q\$). This relationship can be expressed mathematically as \$\Delta U = W + Q\$. This law establishes a fundamental connection between a system's internal energy and the energy transfers that can occur, either through work or heat. It ensures that energy is conserved and cannot be created or destroyed, but only transformed from one form to another.
Describe the role of internal energy in the context of thermal energy and work.
Internal energy is a crucial concept in understanding the relationship between thermal energy and work. Thermal energy, which is the kinetic energy of the particles within a system, is a form of internal energy. Work, on the other hand, is the transfer of energy into or out of a system, and this transfer can change the system's internal energy. The first law of thermodynamics states that the change in a system's internal energy is equal to the sum of the work done on the system and the heat transferred to the system. This means that internal energy can be increased by adding heat to the system or by performing work on the system, and it can be decreased by removing heat from the system or by the system performing work on its surroundings.
Analyze how the internal energy of a system is affected by changes in its state or composition.
The internal energy of a system is a state function, meaning its value depends only on the current state of the system and not on the path taken to reach that state. This means that changes in a system's state, such as its temperature, pressure, or volume, can affect its internal energy. For example, increasing the temperature of a system will increase its internal energy by increasing the kinetic energy of the particles. Similarly, changes in the system's composition, such as the addition or removal of matter, can also affect its internal energy. The first law of thermodynamics provides a framework for understanding how these changes in state or composition can be related to the work done on the system and the heat transferred to or from the system, ultimately affecting the system's internal energy.
Thermal energy is the kinetic energy associated with the random motion of the particles (atoms or molecules) within a substance. It is a form of internal energy and is directly related to the temperature of the system.
Work is the transfer of energy into or out of a system by means of the application of an external force over a distance. It is a form of energy transfer that can change a system's internal energy.
The first law of thermodynamics states that energy can be converted from one form to another, but it cannot be created or destroyed. It establishes a relationship between a system's internal energy, the work done on or by the system, and the heat transferred to or from the system.