Kara Sears
The first law of thermodynamics, also known as the law of conservation of energy, states that energy cannot be created or destroyed but can be converted from one form to another. This means that the total energy in the universe remains constant. The law distinguishes two principal forms of energy transfer in a thermodynamic process: heat and thermodynamic work. It also defines the internal energy of a system, which increases when heat is added and decreases when work is done by the system. This law is foundational for understanding any thermodynamic calculation and is considered the least demanding of the laws of thermodynamics to grasp.
| Characteristics | Values |
|---|---|
| Definition | The first law of thermodynamics is a formulation of the law of conservation of energy in the context of thermodynamic processes. |
| Energy | Energy cannot be created or destroyed, but it can be transformed from one form to another. |
| Total energy of the universe | The total energy of the universe remains constant. |
| Energy balance | Energy balance is developed to better understand any process, to facilitate design and control, to point at the needs for process improvement, and to enable eventual optimization. |
| Work | Work is the force used to transfer energy between a system and its surroundings and is needed to create heat and the transfer of thermal energy. |
| Heat | Heat is the transfer of thermal energy between two bodies that are at different temperatures and is not equal to thermal energy. |
| Internal energy | Internal energy refers to all the energy within a given system, including the kinetic energy of molecules and the energy stored in all of the chemical bonds between molecules. |
| Perpetual motion machines | Perpetual motion machines of the first kind are impossible as work done by a system on its surroundings requires that the system's internal energy be consumed. |
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What You'll Learn
Energy cannot be created or destroyed
The first law of thermodynamics is a formulation of the law of conservation of energy in the context of thermodynamic processes. This law states that energy cannot be created or destroyed, but it can be converted or transferred from one form to another. This principle is also known as the law of conservation of energy.
The first law of thermodynamics distinguishes two principal forms of energy transfer: heat and thermodynamic work. Heat is the transfer of thermal energy between two bodies at different temperatures, while work is the force used to transfer energy between a system and its surroundings. These two concepts are interrelated and allow systems to exchange energy.
The internal energy of a system refers to all the energy within it, including kinetic energy, potential energy, and the energy stored in chemical bonds. The internal energy of a system increases when heat is added or when work is done on the system. Conversely, the internal energy decreases when the system gives off heat or performs work. Since energy cannot be created or destroyed, the change in internal energy always equals zero. This means that any energy lost by the system is absorbed by the surroundings, and vice versa.
The first law of thermodynamics allows for many possible states of a system, but only certain states occur. This leads to the second law of thermodynamics and the concept of entropy, which is related to the randomness or disorder of a system.
In summary, the first law of thermodynamics states that energy cannot be created or destroyed but can only change forms. This law helps us understand the fundamental principles governing energy in the universe and provides a basis for further exploration in thermodynamics and chemistry.
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Energy can be converted from one form to another
The first law of thermodynamics is a formulation of the law of conservation of energy, which states that energy can be converted from one form to another. This principle, also known as the law of energy conservation, asserts that energy cannot be created or destroyed, only transformed. This law is fundamental to our understanding of energy and its role in various processes, including those in the field of chemistry.
In the context of chemistry and thermodynamic processes, the first law of thermodynamics distinguishes two primary forms of energy transfer: heat and thermodynamic work. Heat is the transfer of thermal energy between two bodies at different temperatures, and it is not equal to the thermal energy itself. On the other hand, work is the force required to transfer energy between a system and its surroundings, contributing to the creation of heat and the transfer of thermal energy.
The interplay between heat and work enables systems to exchange energy. This exchange is governed by the first law of thermodynamics, which dictates that the total energy within a system remains constant. For instance, when a driver applies the brakes in a moving car, the kinetic energy of the car's motion is converted into heat energy due to the friction between the brakes and the wheels.
Internal energy, a key concept in the first law, refers to the total energy within a given system. This includes kinetic energy, the energy of motion, and potential energy, which is stored within the system due to its configuration or placement. The internal energy of a system is influenced by changes in heat and work interactions. When heat is added to a system, its internal energy increases, and when work is done on the system, its internal energy also increases. Conversely, if a system performs work or transfers heat to its surroundings, its internal energy decreases.
The first law of thermodynamics underscores the principle that energy is neither created nor destroyed during these transfers and conversions. Instead, energy is conserved, and the change in internal energy within a system is always zero. This law provides a foundation for understanding the behaviour of energy in various processes, including chemical reactions, and serves as a precursor to the second law of thermodynamics, which introduces the concept of entropy.
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The total energy of a system remains constant
The first law of thermodynamics, also referred to as the law of conservation of energy, states that the total energy of a system remains constant. This means that energy cannot be created or destroyed, but it can be converted from one form to another. For example, kinetic energy, the energy of motion, is converted to heat energy when a driver presses the brakes to slow down a car.
The law distinguishes two principal forms of energy transfer in a thermodynamic process: heat and thermodynamic work. Heat is the transfer of thermal energy between two bodies at different temperatures, and work is the force used to transfer energy between a system and its surroundings. Both work and heat allow systems to exchange energy.
The first law also defines internal energy, a state variable that refers to all the energy within a given system, including kinetic energy, potential energy, and the energy stored in chemical bonds. When work is done on or by a system, or when heat is added to or removed from a system, the internal energy of the system changes. However, since energy is conserved, the total energy within the system and its surroundings remains constant. This is known as the energy balance of the system.
The first law of thermodynamics 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. However, it serves as a fundamental concept in understanding and performing any thermodynamic calculation or process.
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Work and heat are interrelated concepts
The first law of thermodynamics is a formulation of the law of conservation of energy in the context of thermodynamic processes. It states that the total energy of a system remains constant, even if it is converted from one form to another. This law is particularly concerned with two principal forms of energy transfer: heat and work.
Work and heat are indeed interrelated concepts. Heat is the transfer of thermal energy between two bodies at different temperatures. Work, on the other hand, is the force used to transfer energy between a system and its surroundings, and it is necessary for creating heat and transferring thermal energy. Work is the primary foundation of thermodynamics and, in particular, the first law. Any system has the capacity to do work. For example, a compressed or extended spring can do work, such as raising a weight. Similarly, an electric battery has the capacity to do work by connecting to an electric motor, which can then be used to raise a weight.
The first law of thermodynamics helps us understand the relationship between work and heat. It also introduces the concept of internal energy, which is all the energy within a given system, including kinetic energy and the energy stored in chemical bonds. When a system gains heat or has work done on it, its internal energy increases. Conversely, when a system loses heat or does work, its internal energy decreases. Importantly, the first law of thermodynamics states that energy cannot be created or destroyed, only converted from one form to another. This means that the change in internal energy of a closed system is equal to the net heat transfer into the system minus the net work done by the system.
The relationship between work and heat can be further understood through the concept of pressure-volume work. Work is equal to the negative external pressure on the system multiplied by the change in volume. This relationship is particularly important in thermodynamics, as it allows for the design and control of processes, as well as the optimisation of energy utilisation.
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Internal energy is a state variable
The first law of thermodynamics is a formulation of the law of conservation of energy in the context of thermodynamic processes. It states that energy can be converted from one form to another, but it cannot be created or destroyed. The total energy of a system remains constant.
Internal energy is affected by factors such as pressure, volume, and temperature. It increases when heat or work is done on a system, and decreases when a system does work or loses heat. The change in internal energy always equals zero, as energy is neither created nor destroyed.
Mathematically, the first law of thermodynamics can be represented as the pressure-volume work, where the work done is equal to the negative external pressure on the system multiplied by the change in volume. This law allows for many possible states of a system, but only certain states occur, leading to the second law of thermodynamics and the definition of another state variable called entropy.
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.
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Frequently asked questions
The first law of thermodynamics states that energy can be converted from one form to another, but it cannot be created or destroyed.
The first law of thermodynamics involves the interaction of three key concepts: heat, work, and internal energy. Heat is the transfer of thermal energy between bodies at different temperatures, and work is the force used to transfer energy between a system and its surroundings. Internal energy refers to the energy within a given system, including kinetic energy and the energy stored in chemical bonds.
The first law of thermodynamics fails to explain the direction of heat flow and the feasibility of processes or changes of state. It also does not account for the quality of energy, treating 1 Watt of heat as equivalent to 1 Watt of work or electricity.
