Keith Mack
The First Law of Thermodynamics is a formulation of the law of conservation of energy in the context of thermodynamic processes. It is defined as the principle that energy is conserved, meaning it cannot be created or destroyed but can be converted among different forms, while the total energy of the universe remains constant. The law distinguishes two principal forms of energy transfer, heat and thermodynamic work, and defines the internal energy of a system. The First Law of Thermodynamics is not capitalized unless it includes a proper noun, such as a person's name.
| Characteristics | Values |
|---|---|
| Definition | The first law of thermodynamics is a formulation of the law of conservation of energy in the context of thermodynamic processes. |
| Energy | Energy cannot be created or destroyed, but it can be transformed from one form to another. |
| Internal Energy | The law defines the internal energy of a system, an extensive property for taking account of the balance of heat transfer, thermodynamic work, and matter transfer, into and out of the system. |
| Perpetual Motion | Perpetual motion machines of the first kind are impossible. |
| Work | Work done by a system on its surroundings requires that the system's internal energy be consumed. |
| Heat | Wherever there is destruction of motive power, there is a simultaneous production of heat in a quantity exactly proportional to the quantity of motive power destroyed. |
| Thermodynamic State Variable | The first law introduces an additional state variable, enthalpy. |
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What You'll Learn
Energy cannot be created or destroyed
The first law of thermodynamics is a formulation of the law of conservation of energy in the context of thermodynamic processes. It states that energy cannot be created or destroyed, but it can be converted from one form to another. This principle is also known as the Law of Conservation of Energy, emphasizing that energy is not created or destroyed but can only change form.
The first explicit statement of the first law of thermodynamics, made by Rudolf Clausius in 1850, referred to cyclic thermodynamic processes and the existence of a function of state of the system, the internal energy. This internal energy is a manifestation of the random molecular motion of the system's constituents. In a closed system, the change in internal energy is equal to the difference between the heat supplied to the system and the work done by the system.
The first law of thermodynamics allows for the understanding of energy balance in any process, facilitating design, control, and process improvement. It also distinguishes two principal forms of energy transfer: heat and thermodynamic work. For example, kinetic energy, the energy of a moving object, is converted to heat energy when a driver presses the brakes to slow down a car.
The first law of thermodynamics also defines the internal energy of a system, taking into account the balance of heat transfer, thermodynamic work, and matter transfer into and out of the system. This law introduces an additional state variable, enthalpy, and allows for the existence of many possible states of a system, although only certain states occur in practice.
The concept of internal energy is central to the first law and distinguishes it from the more general law of conservation of energy. It is important to note that the internal energy of a system can be derived from its overall kinetic energy, potential energy, or internal energy itself. Work, in the context of thermodynamics, refers to the transfer of energy to or from a system, which can be described by macroscopic mechanical forces acting between the system and its surroundings.
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Perpetual motion machines of the first kind are impossible
The first law of thermodynamics is a formulation of the law of conservation of energy in the context of thermodynamic processes. The law states that energy cannot be created or destroyed, only transformed from one form to another. In other words, the total energy of a system remains constant. This law is sometimes taken as the definition of internal energy, which is a function of the state of the system.
Perpetual motion machines of the first kind are those that produce work without the input of energy, thus violating the law of conservation of energy. In other words, they are machines that can do work indefinitely without an external energy source. However, such machines are impossible because their existence would violate the first law of thermodynamics. This is because work done by a system on its surroundings requires that the system's internal energy be consumed, and this energy must be resupplied by an external source.
The history of perpetual motion machines dates back to the Middle Ages, and for a long time, it was not clear whether such devices were possible. Many attempts have been made to create them, including the closed-cycle water mill proposed by Robert Fludd in 1618. However, modern theories of thermodynamics have shown that perpetual motion machines of the first kind are indeed impossible. This is because they violate the fundamental principle that energy cannot be created or destroyed, only transformed.
While it is true that some systems can exhibit near-perpetual motion, such as a machine with a perfect vacuum and no friction, these systems still experience some form of energy loss, such as heat loss. Additionally, these systems still require an initial input of energy, and if energy is extracted from the system, it will eventually come to a stop. Therefore, true perpetual motion machines of the first kind, which require no input of energy and can do work indefinitely, are impossible.
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The internal energy of a system
The first law of thermodynamics is a formulation of the law of conservation of energy in the context of thermodynamic processes. The law defines the internal energy of a system, which is an extensive property that accounts for the balance of heat transfer, thermodynamic work, and matter transfer into and out of the system.
Internal energy refers to all the energy within a given system, encompassing the kinetic energy of molecules and the energy stored in the chemical bonds between molecules. It is a state function or state property, meaning it does not depend on the path taken to reach a particular state. The internal energy of a system increases when heat is added and decreases when the system gives off heat or performs work. Any exchange of heat or work with the surroundings alters the internal energy of the system.
The first explicit statement of the first law of thermodynamics, made by Rudolf Clausius in 1850, included the concept of internal energy. Clausius' statement referred to cyclic thermodynamic processes and the existence of a function of state of the system, the internal energy. He expressed this concept using a differential equation, describing the relationship between the increment in internal energy, heat accumulated by the system, and the thermodynamic work done by the system.
Mathematically, the first law of thermodynamics can be represented as δQ + δW = ΔE, where δQ is the heat added to the system, δW is the work done on the system, and ΔE is the increase in the system's internal energy. This equation illustrates that the change in internal energy is equal to the sum of heat added and work done on the system.
The first law of thermodynamics, also known as the conservation of energy principle, emphasizes that energy cannot be created or destroyed within a system of constant mass. Instead, energy can only be converted from one form to another. This principle applies to both open and closed systems, with energy transfers occurring through mass crossing the control boundary, external work, or heat transfer.
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The principle of conservation of energy
The first law of thermodynamics is a formulation of the principle of conservation of energy in the context of thermodynamic processes. It is defined as the principle that energy is conserved and cannot be created or destroyed. This means that the total energy within a system remains constant, even if it is converted from one form to another. For example, kinetic energy is converted to heat energy when a driver presses the brakes to slow down a car.
The law distinguishes two principal forms of energy transfer: heat and thermodynamic work. It also defines the internal energy of a system, which is an extensive property that accounts for the balance of heat transfer, thermodynamic work, and matter transfer into and out of the system. The internal energy of a system is a manifestation of the random molecular motion of the system's constituents.
The first explicit statement of the first law of thermodynamics, made by Rudolf Clausius in 1850, referred to cyclic thermodynamic processes and the existence of a function of state of the system, the internal energy. He expressed it using a differential equation for the increments of a thermodynamic process. According to this equation, in a thermodynamic process involving a closed system (no transfer of matter), the increment in the internal energy is equal to the difference between the heat accumulated by the system and the thermodynamic work done by it.
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Energy balance
The first law of thermodynamics is a formulation of the law of conservation of energy in the context of thermodynamic processes. The first law of thermodynamics is defined as the principle that energy is conserved, meaning it cannot be created or destroyed but can be converted among different forms, while the total energy of the universe remains constant. This is also known as the Law of the Conservation of Energy. The first explicit statement of the first law of thermodynamics, by Rudolf Clausius in 1850, referred to cyclic thermodynamic processes and the existence of a function of state of the system, the internal energy.
The first law of thermodynamics relates the various forms of kinetic and potential energy in a system to the work that a system can perform and to the transfer of heat. The law distinguishes two principal forms of energy transfer: heat and thermodynamic work. The internal energy of a system is defined as an extensive property for taking account of the balance of heat transfer, thermodynamic work, and matter transfer into and out of the system.
The first law of thermodynamics allows for many possible states of a system to exist. However, experience indicates that only certain states occur. This eventually leads to the second law of thermodynamics and the definition of another state variable called entropy.
The first law of thermodynamics is generally thought to be the least demanding to grasp, as it is an extension of the law of conservation of energy. However, thermodynamics is a subtle subject, and the first law is more interesting than this remark might suggest.
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Frequently asked questions
The First Law of Thermodynamics is a formulation of the law of conservation of energy in the context of thermodynamic processes. It states that energy is conserved, meaning it cannot be created or destroyed, only converted between different forms.
The First Law of Thermodynamics is capitalised as it is a formal name. Proper nouns are usually capitalised.
The equation for the First Law of Thermodynamics is δQ + δW = ΔE, where δQ is the heat added to the system, δW is the work done on the system, and ΔE is the increase of the system's internal energy.
The First Law of Thermodynamics is used to define internal energy, which is a manifestation of the random molecular motion of the system's constituents.
The first explicit statement of the First Law was made by Rudolf Clausius in 1850.
