Cameron Miranda
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. The laws also use various parameters for thermodynamic processes, such as thermodynamic work and heat, and establish relationships between them. Traditionally, there are three fundamental laws, simply named the first law, the second law, and the third law. However, a more fundamental statement was later added and labelled as the zeroth law. The first law of thermodynamics is a version of the law of conservation of energy, which states that energy can be transformed from one form to another, but it cannot be created or destroyed. The second law of thermodynamics states that in a closed system, entropy constantly increases. The third law, also known as Nernst's theorem or Nernst's postulate, was formulated by Walther Nernst between 1906 and 1912. The zeroth law defines thermal equilibrium and forms the basis for the definition of temperature.
| Characteristics | Values |
|---|---|
| First Law of Thermodynamics | Total energy in a closed system is neither lost nor gained — it is only transformed. |
| Second Law of Thermodynamics | Entropy constantly increases in a closed system. |
| Third Law of Thermodynamics | Deals with entropy increases. |
| Zeroth Law of Thermodynamics | Defines thermal equilibrium and forms a basis for the definition of temperature. |
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What You'll Learn
- The First Law of Thermodynamics: Energy can be transferred but not created or destroyed
- The Second Law of Thermodynamics: Entropy increases in a closed system
- The Zeroth Law of Thermodynamics: Defines thermal equilibrium
- The Third Law of Thermodynamics: Deals with entropy increases
- Applications: Thermodynamics in building science
The First Law of Thermodynamics: Energy can be transferred but not created or destroyed
The First Law of Thermodynamics is a version of the law of conservation of energy, which is adapted for thermodynamic processes. This law states that energy can be transferred or transformed from one form to another but cannot be created or destroyed. In other words, the total energy within an isolated system remains constant. This is true even if energy is converted from one form to another.
For example, when cooking a steak on a grill, the First Law of Thermodynamics is at work. Energy is transferred in the form of heat to the steak. Similarly, when we eat, we take in the chemical energy of food and convert it into a form that our body can use to function. This process of energy exchange, where energy transforms from one state to another, occurs within a set of systems and surroundings.
The First Law of Thermodynamics also applies to the energy transformations that occur within simple thermodynamic systems. For instance, energy can be transferred in the form of heat energy (heating and cooling of a substance) or through the production of mechanical work (movement). In biological and chemical terms, this principle can be extended to other forms of energy, such as the chemical energy stored in the bonds between atoms of a molecule or the light energy absorbed by plants.
It is important to note that the transformation of energy is not always 100% efficient. For instance, when electrical energy is transformed into usable light energy, unusable energy in the form of heat is also produced. Despite these transformations and exchanges, the First Law emphasizes that the total energy within a closed system remains unchanged. This law provides a fundamental understanding of energy behaviour in various contexts, from cooking to biological processes.
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The Second Law of Thermodynamics: Entropy increases in a closed system
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. The first law of thermodynamics is a version of the law of conservation of energy, which states that energy can be transformed from one form to another but cannot be created or destroyed.
The second law of thermodynamics states that the total entropy of a closed system either increases or remains constant in any spontaneous process; it never decreases. Entropy can be understood as a measure of the disorder of a system, or a measure of the dispersal of energy. It quantifies how much energy is not available to do work, and the more disordered a system is, the less of its energy can be used to do work. This is because not all energy transferred by heat can be converted into work, and some is lost as waste heat.
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. For example, the first law allows for the possibility of a cup falling off a table and breaking, as well as the reverse process of the fragments coming back together and reassembling on the table. However, the second law allows for the former process but denies the latter.
The second law also predicts that heat transfers energy spontaneously from higher- to lower-temperature objects, but never in the reverse direction. This is because entropy increases for heat transfer from hot to cold. For instance, in the case of melting ice, a highly structured and orderly system of water molecules changes into a disorderly liquid, resulting in an overall increase in entropy.
The second law is a physical law based on universal empirical observation concerning heat and energy interconversions. It is important to note that local and temporal destruction of entropy is impossible, and it cannot be compensated for elsewhere or at a later time. Entropy is always generated and cannot be destroyed by any means.
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The Zeroth Law of Thermodynamics: Defines thermal equilibrium
The Zeroth Law of Thermodynamics is an observation that defines thermal equilibrium. 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 law establishes a mathematical equivalence relation for the concept of thermal equilibrium.
Thermal equilibrium occurs when two bodies are brought into contact with each other and are separated by a barrier that is permeable only to heat, resulting in no transfer of heat between them. This implies that the three bodies are at the same temperature. The Zeroth Law establishes that temperature is a fundamental and measurable property of matter.
The Zeroth Law provides a foundation for the definition of temperature as an empirical parameter in thermodynamic systems. It asserts that thermal equilibrium is a transitive relation between the temperatures of multiple bodies in thermal equilibrium. This law allows for the creation of thermometers, as it justifies the use of empirical temperature as a tagging system.
The Zeroth Law is important for the mathematical formulation of thermodynamics, as it relates thermal equilibrium between systems to an equivalence relation. This mathematical definition of temperature agrees with the physical existence of valid thermometers. The law also provides a basis for the definition of temperature, which is essential to the field of thermodynamics.
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The Third Law of Thermodynamics: Deals with entropy increases
The Third Law of Thermodynamics, also known as Nernst's theorem or Nernst's postulate, was formulated by Walther Nernst between 1906 and 1912. This law deals with entropy increases and defines absolute zero on the entropy scale. According to the Third Law, a perfect crystal at absolute zero (0 Kelvin) will have zero entropy.
A perfect crystal is one with no impurities, having achieved thermodynamic equilibrium, and with a highly ordered crystalline lattice structure. This excludes amorphous solids like glass, which lack a well-defined crystalline structure and have not achieved thermodynamic equilibrium. As the temperature of a perfect crystal increases above absolute zero, the particles within the crystal begin to move, generating disorder, and the entropy of the crystal gradually increases. This increase in entropy is due to the rise in the average kinetic energy of the particles.
The Third Law is significant because it provides a reference point for measuring the absolute entropy of any element or compound. By comparing a substance with a perfect crystal at absolute zero, scientists can determine its absolute entropy. This is particularly useful in chemistry, where the entropy of a system is a critical factor in understanding chemical reactions and their spontaneity.
Furthermore, the Third Law helps us understand the concept of disorder or entropy in isolated systems. In an isolated system, natural processes are spontaneous when they lead to an increase in disorder or entropy. This aligns with the Second Law of Thermodynamics, which states that the entropy of the universe increases in spontaneous processes. As a system deviates from perfection and its temperature rises above absolute zero, the increase in entropy reflects the growing disorder within the system.
In summary, the Third Law of Thermodynamics, concerning entropy increases, provides a definition of absolute zero on the entropy scale and establishes that a perfect crystal at this temperature has zero entropy. This law is essential for measuring absolute entropy and understanding the relationship between temperature, disorder, and spontaneity in isolated systems, contributing to our understanding of chemical reactions and the fundamental principles of thermodynamics.
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Applications: Thermodynamics in building science
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 use various parameters for thermodynamic processes, such as thermodynamic work and heat, and establish relationships between them.
Building science is concerned with heat flow through building enclosures and heat supplied to or removed from conditioned spaces. The laws of thermodynamics lay down the fundamental rules for understanding heat, and that means if you want to understand building science better, you need to know some thermodynamics.
The first law of thermodynamics is a version of the law of conservation of energy, adapted for thermodynamic processes. In a closed system, the first law states that the change in internal energy of the system is equal to the difference between the heat supplied to the system and the work done by the system on its surroundings. This is important in building science because it helps us understand how heat flows through building enclosures. For example, when you turn on an electric kettle in the morning, the water enclosed within the metal container is heated, and the internal energy of the system increases.
The second law of thermodynamics states that in a natural thermodynamic process, the sum of the entropies of the interacting thermodynamic systems never decreases. This has implications for building science because it means that heat does not spontaneously pass from a colder body to a warmer body. This can be observed in the design of heating and cooling systems for buildings, where heat is transferred from a warmer body (the heating system) to a colder body (the building).
The third law of thermodynamics, or Nernst's theorem, deals with entropy increases. This law states that the entropy of a system approaches a constant value as the temperature of the system approaches absolute zero. This has implications for building science in the design of insulation and cooling systems, as well as the study of phase transitions such as the freezing or melting of ice.
The zeroth law of thermodynamics defines thermal equilibrium and forms the 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 law is important in building science because it allows for the consistent measurement of temperature, which is crucial in the design and analysis of building enclosures and HVAC systems.
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