Gavin Howe
The three laws of energy, also known as the laws of thermodynamics, are a set of scientific laws that define a group of physical quantities, such as temperature, energy, and entropy, that characterize thermodynamic systems in thermodynamic equilibrium. The laws also use various parameters for thermodynamic processes, such as thermodynamic work and heat, and establish relationships between them. The first law of thermodynamics, also known as the law of conservation of energy, states that energy cannot be created or destroyed, only changed from one form to another. The second law of thermodynamics, also known as the law of increased entropy, states that over time, the state of disorganization or entropy in a system will always increase. The third law of thermodynamics states that a system's entropy approaches a constant value as the temperature approaches absolute zero. The first law of thermodynamics was formulated by Rudolf Clausius and William Thomson around 1860, and the second law was formulated by Sadi Carnot in 1824. The third law was developed by Walther Nernst from 1906 to 1912.
| Characteristics | Values |
|---|---|
| Number of Laws | 3 |
| First Law | Energy cannot be created or destroyed, only transformed from one form to another. |
| Second Law | The sum of the entropies of the interacting thermodynamic systems never decreases. |
| Third Law | A system's entropy approaches a constant value as the temperature approaches absolute zero. |
| Other Names | The Law of Conservation of Energy, The Law of Increased Entropy |
| Established | 1824 (first law), 1860 (first and second laws), 1906-1912 (third law) |
| Established By | Sadi Carnot (first law), Rudolf Clausius and William Thomson (first and second laws), Walther Nernst (third law) |
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What You'll Learn
The First Law of Thermodynamics
The law was first explicitly stated by Rudolf Clausius in 1850, although its origins can be traced back to earlier works in the 19th century, such as the work of Hermann von Helmholtz and the formulation of Hess's Law by Germain Hess in 1840. The law is a fundamental principle in thermodynamics, which is the scientific study of the interaction of heat and other types of energy.
The law also distinguishes between two principal forms of energy transfer: heat and thermodynamic work. Heat is the transfer of thermal energy between two systems at different temperatures, and work is the force that transfers energy between a system and its surroundings. These two forms of energy transfer are interrelated and allow systems to exchange energy. For example, by producing work within a system, you create heat.
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Energy cannot be created or destroyed
The first of the three laws of energy, also known as the Law of Conservation of Energy, states that energy cannot be created or destroyed. This means that the total amount of energy in the universe is constant. This law was formulated in the 19th and early 20th centuries, with Sadi Carnot, Rudolf Clausius, and William Thomson credited with establishing the first and second laws of thermodynamics by 1860. An earlier statement of the law was made by Karl Friedrich Mohr in 1837, and Christiaan Huygens also contributed to the development of the law in 1669.
The law of conservation of energy is a fundamental principle in physics, stating that energy can only change form. For example, turning on a light switch does not create energy but converts electrical energy into radiant energy (light) and thermal energy (heat). This also applies to the combustion of dynamite, where chemical energy is converted to kinetic energy, potential energy, heat, and sound.
The law of conservation of energy applies to isolated systems, where the total energy within the system can only change through energy entering or leaving. This is distinct from closed systems, where there is no transfer of matter, and the change in internal energy is equal to the difference between the heat supplied and the work done by the system. An example of a closed system is the Earth, which receives energy from the Sun.
The concept of energy conservation is not always well-defined and is dependent on the coordinate system and the type of pseudotensor in use. For instance, the energy exterior to a Kerr-Newman black hole differs when calculated using Møller's pseudotensor compared to the Einstein pseudotensor. However, for practical purposes, energy is conserved in our universe.
The idea that energy cannot be created or destroyed has interesting implications. For example, it suggests that the positive energy required to separate two objects is balanced by negative energy caused by the gravitational attraction between them. This theory implies that matter and energy may cancel each other out, and the Big Bang could have resulted from a simple statistical fluctuation.
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The Second Law of Thermodynamics
The Second Law establishes the concept of entropy as a physical property of a thermodynamic system. It predicts whether processes are forbidden despite obeying the requirement of conservation of energy as expressed in the first law of thermodynamics. It also provides necessary criteria for spontaneous processes. For example, the second law allows for a cup falling off a table and breaking on the floor, but it denies the reverse process of the cup fragments coming back together and jumping back onto the table.
The Second Law can be observed in everyday life. For example, a clean room will eventually become messy, or an ice cube at room temperature will begin to melt. These are examples of how everything leads to an increased state of disorganization or entropy.
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The Third Law of Thermodynamics
In simpler terms, the Third Law states that the entropy of a perfect crystal of a pure substance approaches zero as its temperature approaches zero. This is because, as the energy of the crystal is reduced, the vibrations of its individual atoms are reduced, and the crystal becomes uniform.
The Third Law provides an absolute reference point for determining the entropy of any substance at any temperature. It defines the sign of the entropy of any substance at temperatures above absolute zero as positive. This allows for the measurement of the absolute entropy of any substance at any temperature. The Third Law also implies that a system must have reached its equilibrium state, and therefore its lowest energy, when it cools to the lowest possible temperature.
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The Zeroth Law of Thermodynamics
This law serves as the basis for all temperature measurement. It allows us to justify the use of empirical temperature as a tagging system and provides a mathematical definition of temperature that agrees with the physical existence of valid thermometers. Thermometers, which are used to measure temperature, measure their own temperature. We can say that the temperature T3 of a thermometer is the same as the temperature T1 of a system if the thermometer and system are in thermal equilibrium.
The Zeroth Law also makes the relation of thermal equilibrium between systems an equivalence relation, which can represent equality of some quantity associated with each system. A unique "tag" can be assigned to every system, and if the "tags" of two systems are the same, they are in thermal equilibrium with each other. This property is used to justify the use of empirical temperature as a tagging system.
The Zeroth Law was coined by British physicist and astronomer Ralph H. Fowler when discussing the 1935 text of Saha and Srivastava. The laws of thermodynamics are a set of scientific laws that define a group of physical quantities, such as temperature, energy, and entropy, that characterise thermodynamic systems in thermodynamic equilibrium. They also establish relationships between various parameters for thermodynamic processes, such as thermodynamic work and heat.
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Frequently asked questions
The three laws of energy are also known as the three laws of thermodynamics. The first and second laws were formulated by German physicist Rudolf Clausius and Scottish physicist William Thomson around 1860. The third law was developed by German chemist Walther Nernst from 1906 to 1912.
The first law of thermodynamics, also known as the law of conservation of energy, states that energy cannot be created or destroyed, only changed from one form to another. The second law of thermodynamics, or the law of increased entropy, states that the state of disorganization or entropy in a system will always increase over time. The third law of thermodynamics states that a system's entropy approaches a constant value as the temperature approaches absolute zero.
The first law can be observed when turning on a light switch, which converts electrical energy into radiant energy (light) and thermal energy (heat). The second law can be observed when cooking steak on a grill, as usable energy is converted into unusable energy in the form of heat. The third law is related to the concept of absolute zero, which is a state where no energy is available to do useful work.
