Anaya Nolan
The first law of thermodynamics is a fundamental principle in physics, chemistry, and environmental science. It is a version of the law of conservation of energy, stating that energy cannot be created or destroyed but can be converted between different forms, with the total energy in a closed system remaining constant. This law is essential for understanding energy transfers in various systems, including biological organisms and ecosystems, and forms the basis for the preclusion of certain phenomena, such as perpetual motion. The first law also establishes the concept of internal energy and its relationship to temperature and work done by a system.
| 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 Transfer | Energy can be transferred from one thermodynamic system to another in association with the transfer of matter. |
| Work | Work is a process of transferring energy to or from a system in ways that can be described by macroscopic mechanical forces acting between the system and its surroundings. |
| Heat | Heat is one of the principal forms of energy transfer in a thermodynamic process. |
| Internal Energy | The internal energy of a system is defined by the balance of heat transfer, thermodynamic work, and matter transfer into and out of the system. |
| Conservation of Energy | Energy cannot be created or destroyed, but it can be converted between different forms, and the total energy of the universe remains constant. |
| Perpetual Motion | Perpetual motion machines of the first kind are impossible as work done by a system requires the consumption of the system's internal energy. |
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What You'll Learn
Energy conservation
The first law of thermodynamics is a formulation of the law of conservation of energy in the context of thermodynamic processes. The law of conservation of energy states that energy cannot be created or destroyed, only transformed from one form to another. This is the foundation of energy conservation.
The first law of thermodynamics distinguishes two principal forms of energy transfer: heat and thermodynamic work. Heat is the transfer of thermal energy between two systems or a system and its surroundings due to a temperature difference. Work is a process of transferring energy to or from a system in ways that can be described by macroscopic mechanical forces acting between the system and its surroundings. For example, when a machine lifts an object upwards, energy is transferred from the machine to the object.
The first law also defines the internal energy of a system, which is a function of the state of the system. The internal energy of a system can change through the transfer of heat or work. For example, when a pot of popcorn kernels is placed on a stove, heat is added to the system, and the popcorn does work on its surroundings by lifting the lid of the pot. The internal energy of the system increases as the volume, temperature, and pressure of the popcorn all increase.
The first law of thermodynamics is a fundamental principle in physics and is applicable in various natural sciences, including biology and chemistry. In biological and chemical terms, the concept of energy conservation can be extended to other forms of energy, such as chemical energy stored in the bonds between atoms of a molecule or light energy absorbed by plants.
The first law of thermodynamics also has implications for the design of machines and systems. For example, it implies that perpetual motion machines of the first kind, which produce work with no energy input, are impossible. This is because work done by a system requires that the system's internal energy be consumed, and the amount of energy lost must be resupplied by an external source.
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Heat and thermodynamic work
The first law of thermodynamics is a formulation of the law of conservation of energy in the context of thermodynamic processes. It defines the internal energy of a system, accounting for the balance of heat transfer, thermodynamic work, and matter transfer into and out of the system.
The first law of thermodynamics states that the change in the internal energy of a closed system is equal to the difference between the heat supplied to the system and the work done by the system. Mathematically, this can be represented as ΔU = Q + W, where ΔU is the change in internal energy, Q is the net heat transfer, and W is the net work done.
The sign of Q and W depends on the direction of energy transfer. If Q is positive, there is a net heat transfer into the system, and if W is positive, there is net work done by the system. When energy is transferred from the system to its surroundings, Q and W are assigned a negative sign, and when energy is transferred from the surroundings to the system, they are assigned a positive sign.
The first law of thermodynamics helps us understand the relationship between heat, work, and internal energy. It can also describe how energy transferred by heat can be converted and transferred again by work. For example, in the combustion of coal to produce electricity, the fraction of energy used to perform work is not fixed, and the energy can be released as a mixture of heat and work.
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Internal energy
The first law of thermodynamics is a formulation of the law of conservation of energy in the context of thermodynamic processes. It states that the total energy of a system remains constant, even if it is converted from one form to another. This law is used to categorise the performance of cyclic conversion systems like fossil-fired, steam power cycles, or geothermal cycles.
The internal energy of a system is influenced by changes in heat and work. When a system loses heat or performs work, its internal energy decreases. Conversely, when heat is added to the system or work is done on the system, its internal energy increases. These changes in internal energy are reflected in the mathematical expression of the first law of thermodynamics, where the change in internal energy is equal to the sum of the heat transferred and the work done.
The first explicit statement of the first law of thermodynamics, made by Rudolf Clausius in 1850, referenced cyclic thermodynamic processes and the existence of a function of state of the system, which is the internal energy. This built upon earlier contributions by Émilie du Châtelet in the 18th century, who emphasised the concept of 'vis viva', and the work of Sadi Carnot, who understood the interconvertible nature of heat and "motive power".
In summary, internal energy is a fundamental aspect of the first law of thermodynamics, representing the total energy within a system. The law defines how this internal energy changes through interactions with heat and work, providing a mathematical framework for understanding energy transfers and conversions in various systems, such as a pot of popcorn or a coal combustion process.
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Perpetual motion
The first law of thermodynamics is a formulation of the law of conservation of energy in the context of thermodynamic processes. It states that, when energy passes into or out of a system (as work, heat, or matter), the system's internal energy changes in accordance with the law of conservation of energy. In other words, energy cannot be created or destroyed, but it can be transformed from one form to another.
There are three kinds of perpetual motion machines. The first kind includes those devices that purport to deliver more energy from a falling or turning body than is required to restore the device. These machines violate the first law of thermodynamics, also called the law of conservation of energy, which states that the total energy of a system is always constant. The first such device was suggested by the 13th-century French architect Vilard de Honnecourt. Machines built by Edward Somerset and Johann Bessler in the 17th and 18th centuries, respectively, demonstrated the ability to operate for long periods but could not run indefinitely. Another example of a perpetual motion machine of the first kind is the closed-cycle water mill proposed by English physician Robert Fludd in 1618.
Perpetual-motion machines of the second kind attempt to violate the second law of thermodynamics, which states that some energy is always lost in converting heat into work. One notable failure in this category was the ammonia-filled "zeromotor" developed in the 1880s by John Gamgee.
Perpetual-motion machines of the third kind are those that would supposedly be possible if hindrances like mechanical friction and electrical resistivity could be eliminated. However, such forces can never be completely eliminated without expending additional energy.
The history of perpetual motion machines dates back to the Middle Ages, and despite the scientific consensus that they are impossible, attempts to create them have continued into modern times. The enormous appeal of perpetual motion lies in the promise of a virtually free and limitless source of power.
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Entropy
The first law of thermodynamics defines the relationship between the various forms of kinetic and potential energy present in a system, the work the system can perform, and the transfer of heat. The law states that energy is conserved in all thermodynamic processes—it cannot be created or destroyed, only transformed from one form to another.
The second law of thermodynamics states that if a physical process is irreversible, the entropy of the system and its environment must increase; the final entropy must be greater than the initial entropy. For example, if a hot object is placed in a room, it will quickly spread heat energy in all directions, increasing the entropy of the room. However, if a reversible process occurs, such as forcing a flow through a constricted pipe, the entropy of the system will be zero as variables such as pressure, temperature, and velocity return to their original values downstream of the constriction.
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Frequently asked questions
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.
In the Arctic tundra ecosystem, solar energy is captured by plants through photosynthesis and transformed into chemical energy. Herbivores then consume the plants and obtain this stored chemical energy, and carnivores obtain energy by consuming the herbivores.
The laws of thermodynamics are fundamental laws of physics that characterise thermodynamic systems in thermodynamic equilibrium. They are important in environmental science as they help us understand ecosystems and address environmental problems.
Key terms include energy, internal energy, heat, work, matter, and entropy. The first law distinguishes two principal forms of energy transfer: heat and thermodynamic work. It also defines internal energy as the balance of heat transfer, work, and matter transfer into and out of a system.
