Cecily Zamora
The first law of thermodynamics is a version of the law of conservation of energy, which states that energy cannot be created or destroyed, only converted from one form to another. This law is fundamental to understanding energy transfer and has several corollaries, including Hess's law, which relates to the heat of reaction during chemical transformations, and Faraday's second law of electrolysis. The first law also has implications for the concept of work, which is defined as motion against an opposing force, and is the foundation of the first law. This law also prohibits the existence of perpetual motion machines, which produce work without energy input.
| Characteristics | Values |
|---|---|
| First Law of Thermodynamics | The total energy of a system remains constant, even if it is converted from one form to another. |
| Energy | Cannot be created or destroyed, but can be converted among different forms. |
| Perpetual Motion Machine of the First Kind | Impossible to construct. |
| Work | Motion against an opposing force. |
| Internal Energy | The energy of a system at rest. |
| Hess's Law | A corollary of the first law, stated by Germain Hess in 1840. |
| Temperature | A non-circular definition, without reference to entropy. |
| Energy Balance | Developed to understand and optimise processes. |
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What You'll Learn
Hess's law
The first law of thermodynamics is defined as the principle that energy is conserved and cannot be created or destroyed but can be converted between different forms, while the total energy of the universe remains constant. This is also known as the law of conservation of energy. Hess's law is a corollary of the first law of thermodynamics.
In other words, the total enthalpy change for a reaction is the sum of all changes, regardless of the number of stages or steps in the reaction. This is because enthalpy is a state function, and Hess's law is an expression of this fact. State functions, also known as state quantities, are properties of a system that depend only on the current state of the system, regardless of how the system arrived at that state. Enthalpy is a state function, and so is the total enthalpy change during a chemical reaction independent of the sequence of steps taken.
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Perpetual motion machines of the first kind are impossible
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 the total energy of a system remains constant, even if it is converted from one form to another. For example, kinetic energy is converted to heat energy when a driver presses the brakes to slow down a car. The law also defines 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.
This law has several corollaries, including Hess's law, which is a corollary of the first law of thermodynamics. Another corollary is that perpetual motion machines of the first kind are impossible. This is because work done by a system on its surroundings requires the consumption of the system's internal energy, and this energy must be replenished by an external source. In other words, it is impossible to construct a machine that will perpetually output work without an equal amount of energy input into the machine.
The first law of thermodynamics is generally considered to be the least demanding to grasp, as it is an extension of the law of conservation of energy, which states that energy can be neither created nor destroyed. This means that however much energy existed at the start of the universe, that amount will remain constant. While this may seem straightforward, thermodynamics is a subtle subject, and the first law has many interesting implications.
One of the key implications of the first law is the prohibition of perpetual motion machines of the first kind. These are machines that produce work with no energy input. The idea of a perpetual motion machine has a long history, dating back to ancient theories of heat. However, the first law of thermodynamics demonstrates that such machines are impossible, as they would violate the law of conservation of energy.
While perpetual motion machines of the first kind may seem like a fanciful idea, they have been the subject of serious scientific inquiry. The development of the laws of thermodynamics, including the first law, was a significant achievement that built upon progress made in physics and chemistry over the nineteenth and early twentieth centuries. The first law of thermodynamics, with its prohibition of perpetual motion machines of the first kind, has helped to shape our understanding of energy and its conservation.
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Energy cannot be created or destroyed
The first law of thermodynamics is a version of the law of conservation of energy, which states that energy cannot be created or destroyed. This law, adapted for thermodynamic processes, is also known as the energy balance. It distinguishes two principal forms of energy transfer: heat and thermodynamic work.
The first law of thermodynamics states that the total energy of a system remains constant, even if it is converted from one form to another. For example, kinetic energy—the energy that an object possesses when it moves—is converted to heat energy when a driver presses the brakes on a car to slow down. This is because energy can be transferred from one thermodynamic system to another in association with the transfer of matter.
The first law of thermodynamics is defined as the principle that energy is conserved, meaning it cannot be created or destroyed but can be converted among different forms, while the total energy of the universe remains constant. This means that however much energy there was at the start of the universe, there will be that amount at the end.
The first law of thermodynamics was formulated in the 19th century, with the first explicit statement of the law being made by Rudolf Clausius in 1850. The law is considered the least demanding to grasp out of the laws of thermodynamics, as it is an extension of the law of conservation of energy.
The first law of thermodynamics prohibits the creation of a perpetual motion machine of the first kind, which produces work with no energy input. This is because the work done by a system on its surroundings requires the system's internal energy to be consumed, so the amount of internal energy lost by that work must be resupplied as heat by an external energy source.
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Total energy of a system remains constant
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 the total energy of a system remains constant, even if it is converted from one form to another.
The first law of thermodynamics is defined as the principle that energy is conserved and cannot be created or destroyed. However, it can be converted among different forms, while the total energy of the universe remains constant. In other words, the total energy of an isolated system is always conserved. This means that the total energy within a system will remain the same, even if it is converted into different forms of energy. For example, kinetic energy, which is the energy an object possesses when it moves, is converted into heat energy when a driver presses the brakes to slow down a car.
The first law of thermodynamics relates the various forms of kinetic and potential energy in a system to the work that a system can perform and the transfer of heat. This law is sometimes considered the definition of internal energy and introduces an additional state variable, enthalpy. The internal energy of a system can be changed by the transfer of heat to or from the system or by the system doing work on or having work done on it by its surroundings.
The first law of thermodynamics also allows for many possible states of a system to exist. However, only certain states occur. This eventually leads to the second law of thermodynamics and the definition of another state variable called entropy. Entropy is a measure of the number of possible microscopic configurations or microstates that a system can assume, and it tends to increase in natural processes as energy spreads.
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Energy transfer as heat
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 cannot be created or destroyed, but it can be converted from one form to another. For example, kinetic energy is converted to heat energy when a driver presses the brakes to slow down a car.
The first law of thermodynamics distinguishes two principal forms of energy transfer: heat and thermodynamic work. Work, in the context of thermodynamics, refers to the process of transferring energy to or from a system through mechanical forces. For instance, when a machine lifts a system upwards, energy is transferred from the machine to the system. Another example is the work done by an electric current passing through a heater.
The first law also defines 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 change when energy passes into or out of it as work, heat, or matter. In a closed system, the change in internal energy is equal to the heat supplied to the system minus the work done by the system.
In an adiabatic process, no heat is added or removed from a system. Instead, the change in internal energy is equal to the negative of the work done by the system. An example of an adiabatic process is the rapid expansion of a gas, where there is no transfer of heat, and the temperature decreases as the gas expands against atmospheric pressure.
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Frequently asked questions
The first law of thermodynamics is defined as the principle that energy is conserved. This means that energy cannot be created or destroyed, but it can be converted between different forms. The total energy of a system remains constant.
When a driver presses the brakes in a car to slow down, the car's kinetic energy is converted into heat energy.
The first law of thermodynamics states that a machine that outputs work will require an equal amount of energy input. Therefore, a perpetual motion machine of the first kind, which produces work with no energy input, is impossible.
