Cameron Miranda
The laws of thermodynamics are the result of progress made in this field over the nineteenth and early twentieth centuries. There are three fundamental laws of thermodynamics: the first law, the second law, and the third law. A more fundamental statement was later labelled as the zeroth law after the first three laws had been established. The first law of thermodynamics states that energy can be converted from one form to another but cannot be created or destroyed. The second law of thermodynamics establishes the concept of entropy as a physical property of a thermodynamic system. The third law of thermodynamics states that a system's entropy approaches a constant value as the temperature approaches absolute zero.
| Characteristics | Values |
|---|---|
| First Law of Thermodynamics | Energy can be converted from one form to another with the interaction of heat, work, and internal energy, but it cannot be created nor destroyed, under any circumstances. |
| Second Law of Thermodynamics | The entropy of any isolated system always increases. |
| Third Law of Thermodynamics | The entropy of a system approaches a constant value as the temperature approaches absolute zero. |
| Zeroth Law of Thermodynamics | If two systems are in thermal equilibrium with a third system, the two original systems are in thermal equilibrium with each other. |
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What You'll Learn
- The first law of thermodynamics and the law of conservation of energy
- The second law of thermodynamics and the concept of entropy
- The third law of thermodynamics and the behaviour of entropy at absolute zero
- The zeroth law of thermodynamics and thermal equilibrium
- The history of the laws of thermodynamics
The first law of thermodynamics and the law of conservation of energy
The first law of thermodynamics states that energy can be converted from one form to another, but it cannot be created or destroyed. This is also known as the law of conservation of energy. The law applies to isolated systems, where the sum of all forms of energy must remain constant, even if it has been converted from one form to another. For example, when a machine lifts an object upwards, energy is transferred from the machine to the system.
The first law of thermodynamics provides the definition of the internal energy of a thermodynamic system and expresses its change for a closed system in terms of work and heat. It can be linked to the law of conservation of energy. The law describes the fundamental principle that systems do not consume or 'use up' energy. Instead, energy is converted from one form to another.
The law of conservation of energy states that energy cannot be created or destroyed, only converted from one form to another. This law is fundamental to the understanding of energy and is based on the concept of energy transformation. The law of conservation of energy is a universal principle that applies to all systems, regardless of their specific characteristics.
The first law of thermodynamics is essential for understanding the behaviour of energy in various systems and processes. It provides a foundation for analysing and predicting how energy will be transferred, converted, or conserved within a given system. This law also establishes the concept of internal energy within a thermodynamic system, distinguishing it from the more general law of conservation of energy.
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The second law of thermodynamics and the concept of entropy
The second law of thermodynamics 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. The second law allows for the forward progression of natural processes, but not their reverse. For example, the first law allows for both a cup falling off a table and breaking on the floor, and the reverse process of the cup fragments coming back together and jumping back onto the table. The second law, however, only allows for the former and denies the latter.
The second law of thermodynamics can be stated in three synonymous ways:
- For a spontaneous process, the entropy of the universe increases.
- For a spontaneous process, ΔSuniverse > 0.
- For a spontaneous process, ΔSsystem + ΔSsurroundings > 0.
The last statement of the second law of thermodynamics divides the universe into two parts: the system (what is being investigated) and the surroundings (everything in the universe besides the system). In chemistry, the system is often a chemical reaction under investigation.
The second law states that the entropy of an isolated system always increases. Any isolated system spontaneously evolves towards thermal equilibrium—the state of maximum entropy of the system. The entropy of the universe only increases and never decreases. This is comparable to a room that is not tidied or cleaned, which invariably becomes more messy and disorderly with time. When the room is cleaned, its entropy decreases, but the effort to clean it has resulted in increased entropy outside the room, exceeding the entropy lost.
The second law was historically an empirical finding that was accepted as an axiom of thermodynamic theory. Its first formulation, which preceded the proper definition of entropy and was based on caloric theory, is Carnot's theorem. This was formulated by the French scientist Sadi Carnot, who in 1824 showed that the efficiency of converting heat to work in a heat engine has an upper limit. The first rigorous definition of the second law, based on the concept of entropy, came from German scientist Rudolf Clausius in the 1850s.
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The third law of thermodynamics and the behaviour of entropy at absolute zero
The third law of thermodynamics is concerned with the behaviour of systems as their temperature approaches absolute zero. This law was formulated by Walther Nernst between 1906 and 1912 and is, therefore, often referred to as the Nernst heat theorem.
The third law states that the entropy of a system approaches a constant value as the temperature approaches absolute zero. This constant value is independent of any other parameters characterizing the system, such as pressure or applied magnetic field. At absolute zero (0 Kelvin), the system must be in a state with the minimum possible energy.
Entropy is related to the number of accessible microstates, and there is typically one unique state (the ground state) with minimum energy. In such a case, the entropy at absolute zero will be exactly zero. This is because, at absolute zero, a perfect crystal with no impurities and a well-defined crystalline structure has zero entropy. However, if the system does not have a well-defined order, there may remain some finite entropy as the system is brought to very low temperatures. For example, amorphous solids like glass that don't have an ordered, crystalline structure will still have some entropy at absolute zero.
The third law has implications for the behaviour of entropy at absolute zero. It implies that it is not possible for a process to bring the entropy of a system to zero in a finite number of operations. This is because cooling a system to absolute zero would require an infinite number of steps or an infinite amount of time. Thus, while a temperature of absolute zero does not exist in nature and cannot be achieved in a laboratory, the concept of absolute zero is critical for calculations involving temperature and entropy.
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The zeroth law of thermodynamics and thermal equilibrium
The zeroth law of thermodynamics defines thermal equilibrium and forms a basis for the definition of temperature. It states that if two systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with each other. This concept of thermal equilibrium is fundamental to thermodynamics and was clearly stated in the nineteenth century. The name 'zeroth law' was coined by Ralph H. Fowler in the 1930s, long after the first, second, and third laws were widely recognized.
The zeroth law is essential for understanding temperature and thermal equilibrium. It allows for the definition of temperature in a non-circular way without referring to entropy, its conjugate variable. This law enables the use of thermometers to compare the temperatures of different objects. For example, consider two cups, A and B, both containing boiling water. When a thermometer is placed in cup A, it reaches thermal equilibrium with the water at 100 °C. When the same thermometer is then placed in cup B, it reads the same temperature, indicating that cup B is also at 100 °C. By applying the zeroth law, we can conclude that cups A and B are in thermal equilibrium with each other.
The zeroth law also has implications for the concept of temperature as one-dimensional. It implies that temperature can be arranged in a real number sequence from colder to hotter. This allows for a more comprehensive understanding of temperature and its role in thermodynamics.
Furthermore, the zeroth law is fundamental to the other three laws of thermodynamics. It provides the basis for understanding the first law's principle of energy conservation and the second law's concept of entropy. The zeroth law establishes the foundation for defining the internal energy of a system and its relationship to temperature, as described in the first law. Additionally, it enables the definition of thermodynamic temperature, which is crucial for understanding the second law's focus on the direction of natural processes.
In summary, the zeroth law of thermodynamics is essential for defining thermal equilibrium and temperature in the field of thermodynamics. It has practical applications, such as using thermometers to compare temperatures, and it serves as the foundation for the other three laws, making it a crucial concept in the study of thermodynamics.
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The history of the laws of thermodynamics
The first explicit statement of the first law of thermodynamics was made by Rudolf Clausius in 1850, referring to cyclic thermodynamic processes and the existence of a function of state of the system, the internal energy. In 1851, Thomson introduced the noun "thermo-dynamics" and structured what became thermodynamics with two laws, the first being energy conservation. Thomson also introduced a "second" law, equivalent to Clausius's law that heat cannot flow from cold to hot, based on the principle that heat cannot be completely converted to work.
The first and second laws were formally stated in works 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, with the most accepted version of the law known as the unattainability principle, stating that no process can reach absolute zero temperature in a finite number of steps and within a finite time.
The zeroth law of thermodynamics, which defines thermal equilibrium and forms the basis for the definition of temperature, was named by Ralph H. Fowler in the 1930s.
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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 defines the internal energy of a system and expresses its change for a closed system in terms of work and heat. It also distinguishes between two principal forms of energy transfer: heat and thermodynamic work.
The second law of thermodynamics is a physical law based on universal empirical observation concerning heat and energy interconversions. It states that heat flows spontaneously from hotter to colder regions of matter. It also establishes the concept of entropy as a physical property of a thermodynamic system.
The third law of thermodynamics states that the entropy of a system at absolute zero is constant or that the entropy approaches a constant value as the temperature approaches absolute zero. This constant value is independent of other parameters such as pressure or applied magnetic field.
The second law of thermodynamics was first formulated by French physicist Nicolas Léonard Sadi Carnot in his theoretical analysis of the flow of heat in steam engines in 1824.
A cup falling off a table and breaking on the floor can be allowed by the first law of thermodynamics, as energy is conserved in the process. However, the second law allows the former process but denies the reverse process of the cup fragments coming back together and 'jumping' back onto the table.
