Cecily Zamora
The first law of thermodynamics, also known as the law of conservation of energy, asserts that the total energy of a system and its surroundings is conserved. In other words, energy can be transferred or transformed but cannot be created or destroyed. This law provides a strict energy accounting system, where the change in energy equals the difference between deposits and withdrawals. It is a fundamental principle that governs all thermodynamic processes and has far-reaching implications, such as redefining the concept of energy conservation and providing a mathematical formulation for solving problems in thermodynamics.
| Characteristics | Values |
|---|---|
| Energy transfer | Associated with mass crossing the control boundary, external work, or heat transfer across the boundary |
| Energy balance | The energy balance of a system is affected by the kinetic, potential, internal, and “flow” energies of a fluid |
| Conservation of energy | Energy can be transferred between a system and its surroundings, but it cannot be created or destroyed |
| Energy transformation | Energy can be transformed from one form to another |
| Perpetual motion | Perpetual motion machines of the first kind are impossible |
| Thermal efficiency | The thermal efficiency of a heat engine cannot be greater than 100% |
| Cyclic processes | A cyclic process can be repeated indefinitely, returning the system to its initial state |
| Thermodynamic work | Two principal forms of energy transfer are distinguished: heat and thermodynamic work |
| Internal energy | The internal energy of a system is defined by the balance of heat transfer, thermodynamic work, and matter transfer |
| Thermodynamic equilibrium | The first law of thermodynamics is related to the concepts of temperature and thermal equilibrium |
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What You'll Learn
Energy cannot be created or destroyed
The first law of thermodynamics is a law of conservation of energy. This means that energy cannot be created or destroyed, only transformed from one form to another. The total energy within an isolated system always remains constant.
The first law of thermodynamics is often referred to as the law of conservation of energy. It states that energy can be transferred between a system and its surroundings through the transfer of heat or by the performance of mechanical work. This is also known as the principle of energy conservation. The law is based on the experimental demonstration that heat and mechanical work are interchangeable forms of energy.
The first law of thermodynamics is of great importance and generality. It is a fundamental law of physics and is applicable in other natural sciences. It is a basic concept that underpins many other theories and principles. The law is also of practical use in the design and performance of gas turbines, which are heat engines. As gas turbines convert heat into work, the first law states that we cannot produce more work than the heat supplied.
The first law of thermodynamics is expressed in two ways. One way refers to cyclic processes and the inputs and outputs of the system, but does not refer to incremental changes in the internal state of the system. The other way refers to incremental changes in the internal state of the system and does not require the process to be cyclic.
The first law of thermodynamics is a statement that energy does not simply materialize or disappear. Any gain in energy by the system will correspond to a loss in energy by the surroundings, and vice versa. This is also known as the concept of internal energy.
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Energy can be transferred between systems
The first law of thermodynamics is a version of the law of conservation of energy, which states that energy cannot be created or destroyed, only transformed from one form to another. This law is of great importance and generality and can be understood from several points of view.
The first law of thermodynamics has implications for the transfer of energy between systems. Energy transfer is associated with mass crossing a control boundary, external work, or heat transfer across the boundary, resulting in a change of stored energy within the control volume. For example, 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. This relationship between heat and work was experimentally demonstrated by Mayer and Joule, who found that a quantity of heat is consumed that is proportional to the work done, and vice versa.
The first law also applies to open systems, where there is a transfer of matter. When two initially isolated systems are combined, the total internal energy of the new system is equal to the sum of the internal energies of the two initial systems. This principle was emphasised by French philosopher and mathematician Émilie du Châtelet in the first half of the eighteenth century.
The first law of thermodynamics also has implications for the efficiency of heat engines, which are devices that operate in cycles, producing work from a heat source and rejecting heat to a heat sink. According to the first law, the thermal efficiency of a heat engine, defined as the ratio of the work done to the heat supplied, cannot be greater than 100%.
In summary, the first law of thermodynamics states that energy can be transferred between systems and transformed from one form to another, but it cannot be created or destroyed. This law has important implications for understanding energy transfers and efficiency in both closed and open thermodynamic systems.
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The internal energy of a system can change
The first law of thermodynamics is a conservation law, which means that energy in a system of constant mass can be transferred or converted from one form to another but cannot be created or destroyed. This is often stated as the conservation of energy principle. The first law of thermodynamics is of great importance and generality and is thought of from several points of view.
The first law of thermodynamics defines the internal energy of a system, which is an extensive property for taking account of the balance of heat transfer, thermodynamic work, and matter transfer into and out of the system. The internal energy of a system refers to all the energy within a given system, including the kinetic energy of molecules and the energy stored in all of the chemical bonds between molecules. The internal energy of a system can decrease if the system gives off heat or does work. Conversely, the internal energy of a system increases when the heat increases, which would be done by adding heat to the system. The internal energy would also increase if work were done on the system.
The first law of thermodynamics was formulated in the 19th century, with the first explicit statement of the law made by Rudolf Clausius in 1850. The law was further developed by George H. Bryan in 1907, Constantin Carathéodory in 1909, and Born in 1921. The first law of thermodynamics is a version of the law of conservation of energy, adapted for thermodynamic processes. In a closed system, the change in internal energy is equal to the difference between the heat accumulated by the system and the thermodynamic work done by it.
The first law of thermodynamics is of fundamental importance in physics and other natural sciences. It establishes the concept of internal energy and its relationship to temperature and other forms of energy. The law also provides a basis for the definition of temperature and thermal equilibrium. The law is also essential for understanding and performing any thermodynamic calculation, as it defines the relationship between work and heat, which are interrelated concepts.
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The first law applies to closed systems
The first law of thermodynamics is based on the law of conservation of energy, which states that energy cannot be created or destroyed in a closed system, only transformed from one form to another. This law is of great importance and generality and is typically applied to closed systems.
A closed system is one where there is no transfer of matter into or out of the system. In a closed system, the change in internal energy is equal to the heat supplied to the system, minus the work done by the system on its surroundings. This can be expressed as:
> ΔUsystem = Q - W
Where ΔUsystem is the change in internal energy of the system, Q is the heat supplied to the system, and W is the work done by the system.
The first law of thermodynamics distinguishes between 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 first law was expressed in two ways by Rudolf Clausius in the 19th century. One way refers to cyclic processes and the inputs and outputs of the system, without considering incremental changes in the internal state of the system. The other way refers to incremental changes in the internal state of the system and does not require the process to be cyclic. A cyclic process is one that can be repeated indefinitely, returning the system to its initial state.
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The first law prohibits perpetual motion machines
The First Law of Thermodynamics is based on the law of conservation of energy, which states that energy cannot be created or destroyed, but can be transferred from one form to another. This has profound implications for the operation of machines, prohibiting the creation of perpetual motion machines.
A perpetual motion machine is a hypothetical device that can perform work indefinitely without an external energy source. The first law of thermodynamics makes the existence of such a machine impossible, as it would violate the principle that energy cannot be created or destroyed. Any work done by a system on its surroundings requires a consumption of its internal energy, which must then be replenished by an external source.
The first law of thermodynamics applies to both closed and open systems. In a closed system, there is no transfer of matter, and the law distinguishes between two principal forms of energy transfer: heat and thermodynamic work. For a thermodynamic process to occur, there must be a change in the internal energy of the system, which can be achieved through the addition or removal of heat. However, the law dictates that some heat must leave the system, preventing the infinite generation of heat and, consequently, the perpetual motion of a machine.
In an open system, the distinction between transfers of energy as work and heat is central. The first law prohibits the creation of perpetual motion machines in open systems by establishing the principle that energy cannot be created, only transformed. This means that machines that extract energy from finite sources cannot operate indefinitely, as the energy they are driven by will eventually be exhausted.
The first law of thermodynamics also prohibits a specific type of perpetual motion machine known as the perpetual motion machine of the first kind. This machine purportedly produces work without any energy input, directly violating the law of conservation of energy upheld by the first law. The law's assertion that energy cannot be created means that any work done by a machine requires an input of energy, prohibiting the existence of perpetual motion machines of the first kind.
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