Cecily Zamora
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, also known as the Law of Conservation of Energy, states that energy cannot be created or destroyed, only transferred or converted from one form to another. The second law of thermodynamics deals with entropy and prohibits a perpetual motion machine of the second kind, which spontaneously converts thermal energy into mechanical work. The third law of thermodynamics states that a perfect crystal at zero Kelvin (absolute zero) has zero entropy.
| Characteristics | Values |
|---|---|
| First Law of Thermodynamics | Energy cannot be created or destroyed, only transferred or converted from one form to another. |
| Second Law of Thermodynamics | Entropy constantly increases in a closed system. |
| Third Law of Thermodynamics | A perfect crystal at zero Kelvin (absolute zero) has zero entropy. |
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What You'll Learn
- The first law: energy cannot be created or destroyed
- The second law: entropy increases in a closed system
- The third law: a perfect crystal at absolute zero has zero entropy
- The zeroth law: if two systems are in thermal equilibrium with a third, they are in equilibrium with each other
- Applications: understanding the behaviour of heat and energy
The first law: energy cannot be created or destroyed
The First Law of Thermodynamics, also known as the Law of Conservation of Energy, is a fundamental principle of physics that describes the relationship between energy and heat. It states that energy cannot be created or destroyed, only transferred or converted from one form to another. This law applies to all systems, whether open or closed, and the total amount of energy in a system remains constant even as energy is transferred or converted.
The First Law is based on the understanding that energy exists in various forms, including heat, light, electrical, chemical, and mechanical energy. When energy is transferred or converted, it may change forms, but the total amount of energy remains the same. For example, turning on a light switch does not create energy; it converts electrical energy into radiant energy (light) and thermal energy (heat). Similarly, when you rub your hands together, you generate heat by converting the kinetic energy of your movements into thermal energy, warming your hands.
In a closed system, such as a sealed container with gas inside, the First Law of Thermodynamics dictates that if heat is added to the gas, the temperature of the gas will increase. The resulting increase in temperature causes the gas to expand, performing mechanical work on the surroundings. This demonstrates the interplay between energy and work, where work done on a system can increase its internal energy, while work done by a system can decrease its internal energy.
The First Law also has implications for the natural world and biological systems. For instance, in biological terms, the concept can be extended to chemical energy stored in the bonds between atoms of a molecule or the light energy absorbed by plant leaves through photosynthesis. These processes involve the transfer and conversion of energy without any net gain or loss, adhering to the principle that energy cannot be created or destroyed.
The First Law of Thermodynamics is essential in understanding and designing systems that efficiently convert heat into work. By recognizing that energy is neither created nor destroyed, we can harness and optimize energy transfers and conversions for practical applications, such as generating mechanical work from thermal energy or producing electrical energy from chemical reactions. This law forms the foundation for many scientific and technological advancements, underscoring its significance in various fields, including physics, chemistry, and engineering.
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The second law: entropy increases in a closed system
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. This law is based on universal empirical observation concerning heat and energy interconversions. It establishes the concept of entropy as a physical property of a thermodynamic system.
Entropy is a measure of thermal disorder, or "thermal disorder", and is related to the unavailability of energy to do work. In a closed system, the internal energy of the system is increased by an adiabatic process, during which the volume of the system remains constant. This is because entropy increases for heat transfer from hot to cold. For example, when ice melts, it becomes more disordered and less structured as the systematic arrangement of molecules in a crystal structure is replaced by a more random movement of molecules without fixed locations.
The second law of thermodynamics predicts that it is extremely unlikely for water molecules to reform in the same shape once they have melted and frozen again. This is because the process of melting and freezing involves a transfer of energy, and the second law states that the total entropy of a system will increase or remain constant during such a process.
The second law also has implications for the availability of energy to do work. As a system becomes more disordered, the energy within the system becomes less available to do work. This is because the energy is still in the system, but it is in a form that cannot be used to do work. For example, when two masses of water at different temperatures are mixed, the energy from the hotter water is transferred to the colder water, resulting in an overall increase in entropy. However, once the waters are mixed, there is no more temperature difference to drive energy transfer, and the energy in the water is no longer available to do work.
The second law of thermodynamics is a fundamental principle in the field of thermodynamics, and it has been the subject of much scientific, philosophical, and social discussion. It is one of the three fundamental laws of thermodynamics, which also include the first law (the law of conservation of energy) and the third law (a perfect crystal at absolute zero has zero entropy).
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The third law: a perfect crystal at absolute zero has zero entropy
The first three laws of thermodynamics define a group of physical quantities, such as temperature, energy, and entropy, that characterise thermodynamic systems in thermodynamic equilibrium. The laws also establish relationships between various parameters for thermodynamic processes, such as thermodynamic work and heat.
The Third Law of Thermodynamics states that a perfect crystal at zero Kelvin (absolute zero) has zero entropy. This means that the entropy of a system at absolute zero is constant. In other words, it is impossible for a process to bring the entropy of a given system to zero in a finite number of operations.
A perfect crystal refers to a crystalline state where all atoms, ions, and molecules are in well-defined positions in a highly ordered crystalline lattice. This crystalline structure must have achieved thermodynamic equilibrium, excluding amorphous solids like glass that lack a well-defined structure.
While the Third Law may seem simple and obvious, it is a critical conclusion to a long story about the nature of heat and thermal energy. It is important to note that absolute zero is not attainable in nature or in laboratories, but it is a critical concept for calculations involving temperature and entropy. As the temperature of a system approaches absolute zero, the extraction of energy becomes increasingly difficult, tending towards infinity.
The Third Law has implications for the calculation of the absolute entropy of a substance at any temperature. These calculations are based on heat capacity measurements, allowing for the determination of the absolute entropy of a solid at a given temperature.
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The zeroth law: if two systems are in thermal equilibrium with a third, they are in equilibrium with each other
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.
The Zeroth Law of Thermodynamics defines thermal equilibrium and forms a basis for the definition of temperature. It states that if two systems are in thermal equilibrium with a third system, then they are in thermal equilibrium with each other. This law allows for the definition of temperature in a non-circular way without reference to entropy, its conjugate variable. Such a temperature definition is said to be 'empirical'.
The Zeroth Law allows us to define the direction of heat flow between systems. If we know the temperature of a set of connected systems, we can determine the direction of heat flow based on the fundamentals of thermal equilibrium. This law also makes it meaningful to use thermometers as the "third body" and to define a temperature scale.
The Zeroth Law is a more fundamental statement that was labelled as such after the first three laws had been established. The name ""Zeroth Law" was invented by Ralph H. Fowler in the 1930s, long after the first, second, and third laws were widely recognised.
The Zeroth Law is foundational to the other three laws and is considered a basic understanding that was always thought to be true but needed to be formally stated. It is also referred to as an additional law that was needed to fully describe energy changes in systems.
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Applications: understanding the behaviour of heat and energy
The laws of thermodynamics are a set of scientific principles that define a group of physical quantities, such as temperature, energy, and entropy, which 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.
The first law of thermodynamics, also known as the Law of Conservation of Energy, states that energy cannot be created or destroyed. In other words, the total energy of the universe must remain constant. Energy can be transferred between a system and its surroundings through the transfer of heat or by the performance of mechanical work. For example, when you turn on a light switch, electrical energy is converted into radiant energy (light) and thermal energy (heat).
The second law of thermodynamics deals with entropy and states that in a natural thermodynamic process, the sum of the entropies of the interacting thermodynamic systems never decreases. In other words, the entropy of a spontaneous process must increase. This means that heat does not spontaneously pass from a colder body to a warmer body. An example of the second law in action is the heating and subsequent cooling of food in an oven.
The third law of thermodynamics states that a perfect crystal at zero Kelvin (absolute zero) has zero entropy. A perfect crystal has no impurities, has achieved thermodynamic equilibrium, and has a highly ordered crystalline lattice structure. This law implies that a perfect crystal at absolute zero must exist in a single microstate.
The laws of thermodynamics help us understand the behaviour of heat and energy and allow us to design systems that can efficiently convert heat into work. For example, in a car engine, the laws of thermodynamics describe how heat is converted into the work of moving the pistons, which in turn move the car. Similarly, in a refrigerator, the laws of thermodynamics describe how heat is removed from the inside of the fridge and transferred to the outside, thereby cooling the contents.
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Frequently asked questions
The first law of thermodynamics, also known as the Law of Conservation of Energy, states that energy cannot be created or destroyed, only transferred or converted from one form to another.
The second law of thermodynamics deals with entropy and states that in a natural thermodynamic process, the sum of the entropies of the interacting thermodynamic systems never decreases. A common corollary of the statement is that heat does not spontaneously pass from a colder body to a warmer body.
The third law of thermodynamics states that a perfect crystal at zero Kelvin (absolute zero) has zero entropy.
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.
The first and second laws prohibit two kinds of perpetual motion machines, respectively. The first law prohibits a perpetual motion machine of the first kind which produces work with no energy input. The second law prohibits a perpetual motion machine of the second kind which spontaneously converts thermal energy into mechanical work.
