Cecily Zamora
The First Law of Thermodynamics is commonly referred to as the Law of Conservation of Energy. This law of conservation is a fundamental concept in physics and engineering, and it states that energy cannot be created or destroyed, only converted from one form to another. For instance, potential energy can be converted to kinetic energy, but the total energy within a domain remains fixed. The First Law of Thermodynamics evolved from the experimental demonstration that heat and mechanical work are interchangeable forms of energy.
| Characteristics | Values |
|---|---|
| Definition | The first law of thermodynamics is defined as the principle that energy is conserved. |
| Other Names | Conservation of energy, Law of Conservation of Energy |
| Energy | Energy can neither be created nor destroyed, but can be converted among different forms. |
| Total Energy | The total energy of the universe remains constant. |
| Energy Transfer | Energy can be transferred from one thermodynamic system to another. |
| Work | Work is the movement of matter when a force is applied to it. |
| Heat | Heat is one of the principal forms of energy transfer. |
| Internal Energy | The first law of thermodynamics defines the internal energy of a system. |
| Enthalpy | A useful additional variable is the specific enthalpy (h), the sum of the internal energy and the pressure-volume term used to define the work on the gas. |
| Entropy | One of the four fundamental functions of thermodynamics described by the first law. |
| Helmholtz Free Energy | One of the four fundamental functions of thermodynamics described by the first law. |
| Gibbs Free Energy | One of the four fundamental functions of thermodynamics described by the first law. |
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What You'll Learn
Energy cannot be created or destroyed
The first law of thermodynamics, also known as the law of conservation of energy, states that energy cannot be created or destroyed. This means that the total energy in a closed system is constant—it can only change when energy enters or leaves the system. The principle, which evolved from the experimental demonstration that heat and mechanical work are interchangeable forms of energy, is considered the least demanding of the laws of thermodynamics to grasp.
The law of conservation of energy is a fundamental concept in physics, alongside the conservation of mass and the conservation of momentum. It implies that mass can be converted to energy and vice versa. This is observed in the nuclear binding energy of atomic nuclei, where a mass defect is measured. Mass-energy equivalence is believed to become important in extreme physical conditions, such as those that existed shortly after the Big Bang or when black holes emit Hawking radiation.
The conservation of energy was first generally stated by Karl Friedrich Mohr in 1837, who wrote:
> Besides the 54 known chemical elements there is in the physical world one agent only, and this is called Kraft [energy or work]. It may appear, according to circumstances, as motion, chemical affinity, cohesion, electricity, light and magnetism; and from any one of these forms, it can be transformed into any of the others.
This principle was later echoed by Albert Einstein, who famously said, "Energy cannot be created or destroyed, it can only be changed from one form to another."
While the law of conservation of energy is considered a fundamental principle of physics, there are some metrics, such as the Friedmann–Lemaître–Robertson–Walker metric, that do not satisfy its constraints. For example, pseudotensor energy is dependent on the type of pseudotensor in use, and so energy conservation is not well defined. However, for practical purposes, energy is considered to be conserved in our universe.
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Energy can be converted from one form to another
The First Law of Thermodynamics is commonly referred to as the Conservation of Energy. This law states that energy cannot be created or destroyed, only altered in form. In other words, energy can be converted from one form to another. This principle is fundamental to physics and is observed in various natural phenomena and human-made machines.
Energy conversion, also known as energy transformation, is the process of changing energy from one form to another. This principle is illustrated through various examples, such as the conversion of kinetic energy to thermal energy and chemical energy to thermal energy. For instance, when a moving object, like a car, comes to a stop, its kinetic energy is transformed into thermal energy due to friction. Similarly, in a combustion engine, the chemical energy stored in the fuel is converted into thermal energy when the fuel burns, producing heat.
There are numerous other examples of energy conversion in machines and transducers. For instance, in a battery, chemical energy is converted into electrical energy. An electric generator transforms kinetic energy or mechanical work into electrical energy. In coal-fired power plants, the chemical energy in the coal is converted into electrical energy through a series of transformations. First, the chemical energy in the coal is converted into thermal energy through combustion. Then, the thermal energy of the exhaust gases is transferred to steam via a heat exchanger. Finally, the thermal energy of the steam is converted into mechanical energy in a turbine.
Energy conversion is also observed in natural phenomena, such as weather events. For example, sunlight is a form of energy that can be captured and converted by plants into chemical potential energy through photosynthesis. Sunlight also drives many weather phenomena, such as hurricanes, which are formed when warm ocean waters suddenly release thermal energy to power violent air movements.
The First Law of Thermodynamics evolved from the experimental demonstration that heat and mechanical work are interchangeable forms of energy. This law is expressed mathematically through differential equations that describe the energy states of a system, including entropy, enthalpy, Helmholtz free energy, and Gibbs free energy. These functions, along with calculus and differential equations, can be used to understand the thermodynamic properties of any system.
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The internal energy of a system
The first law of thermodynamics, also known as the conservation of energy principle, states that energy can neither be created nor destroyed, only altered in form. This means that the total energy within a system always remains constant, although it may be converted from one form to another. For instance, potential energy can be converted to kinetic energy.
The internal energy within a system can be associated with the motion of particles and can be added to the system. This is referred to as thermal energy, which is the total kinetic energy of the particles within a substance. When energy is added to a system without causing a phase change, it results in greater motion of the particles and an increase in temperature. However, if the energy added is greater than the threshold energy, it can cause a phase change in the substance.
The first law of thermodynamics helps to clarify the meaning of internal energy within a system. The change in internal energy is equal to heat transfer minus the work done on the system. This can be simplified using the enthalpy of the gas, which is the sum of the internal energy and the pressure-volume term used to define the work on the gas.
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The first law is an extension of the law of conservation of energy
The first law of thermodynamics is a fundamental concept in physics and engineering, and it is commonly referred to as the law of conservation of energy. This law states that energy cannot be created or destroyed, only altered from one form to another. For instance, potential energy can be converted to kinetic energy, but the total energy within a system remains constant. This principle is known as the conservation of energy.
The first law of thermodynamics is an extension of this principle, applied specifically to thermodynamic processes. It distinguishes between two principal forms of energy transfer: heat and thermodynamic work. The law also defines the internal energy of a system, which is an important variable in thermodynamics. The internal energy of a system is affected by heat transfer, work done on the system, and matter transfer into and out of the system.
The first law of thermodynamics evolved from experimental demonstrations that heat and mechanical work are interchangeable forms of energy. This was first stated by Julius Robert von Mayer in 1842, who said that "in a process at constant pressure, the heat used to produce expansion is universally interconvertible with work". This statement, along with the work of other scientists such as Germain Hess and James Prescott Joule, laid the foundation for the first law of thermodynamics.
The law of conservation of energy can be applied to a variety of systems beyond just thermodynamics. It is a fundamental concept in physics, along with the conservation of mass and momentum. In the context of thermodynamics, the law of conservation of energy helps to explain the thermal properties of systems and the transfer of energy between them. This transfer of energy can occur through various pathways, including adiabatic and non-adiabatic processes, and can be accompanied by the transfer of matter.
Overall, the first law of thermodynamics is a crucial concept in understanding the behaviour of energy in closed systems. It is an extension of the more general law of conservation of energy, providing specific insights into the thermal dynamics of energy transfer and transformation. By applying the first law, scientists can describe and predict the behaviour of energy in a wide range of systems, from mechanical systems to the universe as a whole.
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Applications in thermodynamic processes
The first law of thermodynamics is a fundamental concept in physics, stating that energy is conserved and cannot be created or destroyed, only converted from one form to another. This principle, also known as the Law of Energy Conservation, has various applications in thermodynamic processes, which are guided by the concept of energy conservation.
One of the key applications of the first law of thermodynamics is in understanding and analyzing energy transfers and conversions within a system. According to the first law, when a system undergoes a change due to the interaction of heat, work, and internal energy, there is a series of energy transfers and conversions. However, there is no net change in the total energy within the system. This concept is crucial for analyzing and designing thermodynamic processes, as it allows for a precise energy balance to be maintained.
The first law also helps define 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 can be affected by changes in pressure, volume, and temperature. For example, in a closed system, if work is performed on the system, its internal energy increases, and when work is performed by the system, its internal energy decreases.
Additionally, the first law of thermodynamics has implications for cyclic thermodynamic processes. Rudolf Clausius, in 1850, expressed the first law in the context of cyclic processes, considering the inputs and outputs of the system without referring to incremental changes in the internal state. This formulation highlights the necessity of heat transfer into and out of the system during a cyclic process.
Furthermore, the first law of thermodynamics provides a foundation for understanding the feasibility of various processes. While the first law itself does not determine the feasibility, it quantifies the amount of energy transferred during a process. This information can then be used to assess the feasibility of a process based on energy considerations.
Overall, the first law of thermodynamics, with its principle of energy conservation, is essential for understanding and optimizing thermodynamic processes. It provides a framework for analyzing energy transfers, conversions, and balances within a system, guiding the design and control of processes, and facilitating comparisons between different systems.
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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.
The first law of thermodynamics states that energy can neither be created nor destroyed, only altered in form.
Burning wood is an example of the first law of thermodynamics. The energy we see in the form of fire is not created out of nothing but comes from the energy stored in the wood.
The law of conservation of energy is a fundamental concept in physics and engineering, which states that energy can be converted from one form to another but the total amount of energy remains constant.
The first law of thermodynamics is an extension of the law of conservation of energy. It applies the principle of energy conservation to thermodynamic systems, distinguishing between heat and thermodynamic work as forms of energy transfer.
