# Entropy and the Laws of Thermodynamics

• Physics345
In summary: In this case, the mechanism of heat transfer would be radiation (energy coming in contact with the molecules), and as the system reaches a thermodynamic equilibrium of ten degrees Celsius, the entropy of the universe would have decreased by one degree Celsius. Since the entropy of the universe cannot decrease, this means that the second law of thermodynamics is violated. This implies that the universe is in a state of disorder, which is opposite of thermodynamic equilibrium. Now that we have established how entropy relates to the two laws of thermodynamics, we can move on to discussing energy. Energy is described as the ability to do work. To do work, we
Physics345
Homework Statement
The purpose of this assignment is to make connections between entropy, energy, and work. To achieve this, you will define energy and explain why it is useful to us. You will also discuss how engineers transform energy from the environment into forms useful for human endeavors. This will require that you explain both thermodynamics, and entropy. You will also outline each of the four laws and provide explanations and examples of each. You will then outline and define the four branches of thermodynamics. In this outline, you will include:
• a list of the methodological approaches used in conjunction with each branch,
• a list the theories associated with each branch,
• the contributions each branch makes to the understanding of thermodynamics,
• any perceived limitations to each of the branches, and
• an explanation of how entropy is understood/explained in each respective branch.
Your conclusion will summarize your key points and explain the importance of understanding thermodynamics in the contemporary world. As this paper is more of a report than an essay, an overt argument is not required
Relevant Equations
No equations required.
Hello everyone,

I have to write a paper about entropy and how it relates to the laws of thermodynamics, energy, and work. I have taken a deductive approach starting from the zero-th law to the second law of thermodynamics as follows.

Entropy is the disorder of a system (Class Video, 2019). To describe entropy, let’s begin by discussing what a system is. A system can be described as any mass which consists of molecules. A room, moon, planet, sun, galaxy, and the universe are all systems. They all comprise molecules but what drives these molecules to become disordered? Well, let’s think of boiling water, the system would be the pot that boils the water. As the water increases in temperature, the molecules begin to collide at a much faster rate, which implies an increase in entropy. When one closes their eyes and imagines millions of molecules colliding with one another, would they refer to this state as ordered or disordered? It would be disordered. For the molecules to be in order, they would need to halt their motion. Therefore, a state of order would be when molecules are no longer in motion, and a state of disorder is when the molecules are in motion. Then it also goes to say, that when heat is transferred, there is a disorder in a system and when the heat is not being transferred, there is order in a system. This means energy will always exist in the universe, but energy requires heat to be transferred from one body to another. Therefore, without heat being transferred in a system work cannot occur. Now that we have established what entropy is let’s continue by deducing how it relates to the laws of thermodynamics. We will begin with the zero-th law of thermodynamics which states “if two bodies are equal in temperature to a third, they are equal in temperature to each other” (Oakes, 2016, pg. 506). When one thinks of how the universe transfers heat, they will think of stars and radiation. Then how does the zero-th law and entropy relate to one another? When the universe reaches absolute zero, the zero-th law applies. If there is heat being transferred in the universe, then there will be disorder. If heat is no longer being transferred in the universe, then the universe will reach a state of order. All life will cease, to exist since all bodies within the universe will be equal in temperature, of absolute zero. This implies no heat is being transferred in the universe thus reaching a thermodynamic equilibrium. A thermodynamic equilibrium occurs “when the properties do not vary from point to point in a system and there is no tendency for change”. Following the definition, we can conclude that this is an isothermal process. This means that the surface temperature is constant, the ambient temperatures are constant. Therefore, all temperatures are equal to absolute zero. This implies the energy being transferred during thermodynamic equilibrium should equal zero, when heat is no longer being transferred, molecules can no longer collide; therefore work can no longer occur. This means the end of heat transfer within the universe, thus the end of all life as we know it. The first law of thermodynamics states “During a given process, the net heat transfer minus the network output equals the change in energy” (Oakes, 2016, pg. 506). This tells us that energy can be converted from A to B. This implies that energy is always being transferred with an increase in disorder (entropy), thus achieved with an increase in heat transfer. If energy is always being transferred, then energy cannot be created or destroyed. Therefore, energy will always exist but without heat-transfer, energy can no longer be transferred from one body to another as described in the zero-th law. For example, let’s say we had an insulated system comprising two bodies. Assume the insulation is thick enough to not allow heat transfer inside and outside of the system. During this example, we will neglect radiation. Then let’s say body (A) has a temperature of zero degrees Celsius. This body then comes in contact with another body (B) that has a temperature of twenty degrees Celsius within the isolated system. In this case, the mechanism of heat transfer would be conduction (two bodies coming in contact with each other), and the heat will transfer from B to A until they reach a thermodynamic equilibrium of ten degrees Celsius. Since the system is being isolated by insulation, it would be an adiabatic process (Oakes, 2016, pg. 506). Let’s now consider the second law of thermodynamics which states “During a process, the net entropy of the universe cannot decrease” (Oakes, 2016, pg. 506). To deduce the meaning of the law, let’s consider the two insulated bodies discussed previously except this time the bodies will not come into contact with each other and radiation occurs. Before body (B) is placed into the closed system, which contained a body (A), the temperature of the system stays at a constant of zero degrees Celsius. This also means that the entropy is relative to this temperature and is also constant. When the entropy is constant, we refer to it as an isentropic process (Oakes, 2016, pg. 506). Once body (B) which has a temperature of twenty degrees Celsius is placed within the closed system, then radiation will transfer body (B)'s heat throughout the system. When this process occurs the entropy of the system can only increase because the heat is being distributed throughout the system. Eventually, the system will reach a state of thermodynamic equilibrium of ten degrees Celsius, but before reaching this state the process of heat transfer must occur. During the process, the entropy can only increase until the system reaches a thermodynamic equilibrium at which point (A) and (B) will be ten degrees Celsius. Therefore, the process of heat transfer can only increase entropy until the process reaches a thermodynamic equilibrium.

This is my first time dealing with thermodynamics so please excuse my ignorance. I appreciate all forms of constructive criticism. Also, I know that I have not covered all the points required by the assignment. I wanted to ensure this part is correct before completing the rest.

Thank you,

Delta2
Oops, I just realized there is a third law that describes the absolute minimum temperature that I related to the zeroth law. Wait, that's odd does that mean the zeroth law allowed physicists to realize the third Law or did I misunderstand the zeroth law?

Hello everyone,

I made some changes they are as follows:
To describe entropy, let’s begin by discussing what a system is. We can describe a system as any mass which comprises molecules. A room, moon, planet, sun, galaxy, and the universe are all systems. To visually describe entropy one can close their eyes and imagine millions of molecules colliding with one another, would they refer to this state as ordered or disordered? For the molecules to be in order, they would need to synchronize their motion. Therefore, a state of order would be when molecules are in synchronized motion, and a state of disorder is when the molecules are in unsynchronized motion. Then it also goes to say, when heat is transferred, the system is in disorder, and when heat is not being transferred, there is order in a system. This means energy will always exist in the universe, but energy requires heat to transfer from one body to another. Therefore, without heat being transferred in a system work cannot occur. Without work energy cannot be transferred, thus also cannot be transformed. To describe this process, let’s think of boiling water. The system would be the stove (body A), pot (body B), and water (body C). As long as the stove stays at a constant temperature, it would be an isothermal process of heat transfer described by Fourier’s Law of Conduction. Conduction occurs when surfaces of varying temperatures are in physical contact with one another. Energy “is stored as internal energy, kinetic energy, and potential energy; then transforms between these three forms; and transferred as work or heat transfer” (Oakes, 2018, pg. 506). In the example, work transfers the internal thermal energy from the hot surface area of the stove to the cooler surface area of the pot; the pot stores the transferred energy, transforming it into potential thermal kinetic energy which is transferred through the body of water. This process causes the water molecules to collide at a rapid rate and the entropy of all the molecules within the system to increase relative to the potential thermal energy of the stove (body A) until all the molecules involved in the system reach a state of thermodynamic equilibrium. A thermodynamic equilibrium occurs “when the properties do not vary from point to point in a system and there is no tendency for change” (Oakes, 2018, pg. 506). This means all the molecules within the system will collide at the same rate and in the same motion because they have reached a constant temperature and entropy. At this point, entropy is no longer increasing and the excess thermal energy will dissipate throughout the universe. This process serves as an example of the zeroth law of thermodynamics which states “if two bodies are equal in temperature to a third, they are equal in temperature to each other” (Oakes, 2018, pg. 506). Therefore, once this system reaches a thermodynamic equilibrium, the stove, pot, and water will all be equal in temperature to each other.

The first law of thermodynamics states “During a given process, the net heat transfer minus the network output equals the change in energy” (Oakes, 2018, pg. 506). This tells us that energy can convert from (A) to (B). This implies that energy is always being transferred with an increase in disorder (entropy), thus achieved with an increase in heat transfer. If energy is always being transferred, then energy cannot be created or destroyed. Therefore, energy will always exist but without heat-transfer, energy can no longer be transferred from one body to another as described in the zeroth law. For example, let’s say we had an insulated system comprising two bodies (A) and (B). Assume the insulation is thick enough to not allow heat to transfer inside and outside of the system. During this example, we will neglect radiation. Then let’s say body (A) has a temperature of zero degrees Celsius. This body then comes in contact with another body (B) that has a temperature of twenty degrees Celsius within the isolated system. In this case, the mechanism of heat transfer would be conduction, and the heat will transfer from B to A until they reach a thermodynamic equilibrium of ten degrees Celsius. Since the system is being isolated by insulation, it would be an adiabatic process (Oakes, 2018, pg. 506). The first law also describes the ideal gas law and an isobaric process. Let’s consider the previous example of the boiling water again to describe this process. I previously described the energy being dissipated throughout the universe, but never explained why and how this occurs. As the temperature of the stove, pot, and water reach thermodynamic equilibrium, the build-up in pressure becomes relative to the increase in temperature ("Isobaric Process: Thermodynamic Processes"). Let’s say that we expose the pot of water to the surrounding air, in this case, the water molecules will collide at a rapid rate. This will cause the pressure of the water to become constant and thus make it an isobaric process (Oakes, 2018, pg. 506). With the build-up of constant pressure, the molecules will expand to dissipate the kinetic energy ("Isobaric Process: Thermodynamic Processes"). This process is best described by Charles’s law, it states “The volume varies directly with temperature for an ideal gas” (Oakes, 2018, pg. 506). From here we can conclude that the liquid water expands in volume, thus releasing the excess temperature by dissipating water vapour into the air and thus drifts into the universe ("Isobaric Process: Thermodynamic Processes"). However, what happens when the boiling water is sealed? The volume will remain constant since the water vapour cannot escape from the system. This process is an isometric process. When the volume of the water vapour cannot escape the sealed system, the pressure will act on the sealed container and dissipate internal energy (pressure) against the walls of the container. The internal energy will constantly be bombarding against the sealed container until the material can no longer sustain the pressure and explodes.

Let’s now consider the second law of thermodynamics which states “During a process, the net entropy of the universe cannot decrease” (Oakes, 2018, pg. 506). To deduce the meaning of the law, let’s consider the two insulated bodies discussed previously except this time the bodies will not come into contact with each other, radiation occurs, and the closed system is being insulated by the universe. For sake of clarity let’s say the universe comprises two bodies (A) zero degrees Celsius and (B) twenty degrees Celsius. Before body (B) is placed into the closed system, which contained a body (A), the temperature of the system stays at a constant of zero degrees Celsius. This also means that the entropy is relative to this temperature and is also constant. When the entropy is constant, we refer to it as an isentropic process (Oakes, 2016, pg. 506). Once body (B) is placed within the closed system, then radiation will transfer body (B)'s heat throughout the system and hence increasing the entropy of the system because the heat is being distributed throughout the closed system. Eventually, the system will reach a state of thermodynamic equilibrium of ten degrees Celsius, but before reaching this state the process of heat transfer must occur. During the process, the entropy can only increase until the system reaches a thermodynamic equilibrium at which point (A) and (B) will be ten degrees Celsius. From here we get a rough idea of how the second law of thermodynamics works. The universe traps all the thermal heat its bodies produce by work within it. The process of work and heat transfer can only increase the entropy of the universe. As long as work exists in the universe, it will dissipate thermal energy throughout the universe and will have nowhere to escape. From here we can conclude that the universe will always have an increase of entropy until it reaches a relative maximum thermodynamic equilibrium. As long as work exists in the universe there will be an increase of temperature and thus an increase in entropy. For the universe to reach a thermodynamic equilibrium would imply all forms of potential energy in the universe have been dissipated back into it. At this point work will no longer exist in the universe; thus the entropy cans no longer increase, this means the entropy will becomes constant and dissipates throughout the universe until it reaches a thermodynamic equilibrium.

The third law of thermodynamics states “The entropy of a system approaches a constant value as the temperature approaches absolute zero” (Kittel & Krömer, 1980). This follows the second law of thermodynamics since the entropy of the universe will never reach a state of thermodynamic equilibrium unless energy is no longer being transferred through work. Therefore, once the maximum thermodynamic equilibrium occurs the universe will equally dissipate its thermal energy until it reaches a value of constant entropy. This only occurs as the temperature of the universe approaches zero Kelvin. However, when one considers the second law of thermodynamics, they will realize that the third law acts as a restriction. If the universe is a closed system, then the system will always have some thermal energy. Therefore, the universe will never reach a temperature of absolute zero unless the thermal energy can escape the system. Then if that’s the case we can further conclude that the thermal energy will just dissipate throughout the universe equalizing at some temperature close to absolute zero. To say that the universe can reach absolute zero would imply the universe is not a closed system and is within another system. As far as we know that is not the case.

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I have made my final edits, it looks

To describe entropy, let’s begin by discussing what a system is. We can describe a system as any mass which comprises molecules. A room, moon, planet, sun, galaxy, and the universe are all systems. To visually describe entropy one can close their eyes and imagine millions of molecules colliding with one another. For the molecules to be in order, they would need to synchronize their motion or idleness. Therefore, a state of order would be when molecules are in synchronized motion or idleness, and a state of disorder is when the molecules are in unsynchronized motion. Then it also goes to say, when heat transfers into the system, it is in disorder, and when heat is no longer being transferred, the system reaches a state of order. This means thermal energy will always exist in the universe, but it requires work to transfer heat from one body to another. Therefore, without work energy cannot transfer, thus also cannot transform. To describe this process, let’s think of boiling water. The system would be the stove (body A), pot (body B), and water (body C). During the process energy “is stored as internal energy, kinetic energy, and potential energy; then transforms between these three forms; and transferred as work or heat transfer” (Oakes, 2018, pg. 506). In the example, work transfers the internal thermal energy from the hot surface area of the stove to the cooler surface area of the pot by radiation; the pot stores the transferred energy by conduction transforming it into thermal kinetic energy that convection transfers through the body of water. This process causes the water molecules to collide at a rapid rate and the entropy of all the molecules within the system to increase relative to the potential thermal energy of the stove until all the molecules involved in the system reach a state of thermodynamic equilibrium. A thermodynamic equilibrium occurs “when the properties do not vary from point to point in a system and there is no tendency for change” (Oakes, 2018, pg. 506). This means all the molecules within the system will collide at the same rate and in the same motion because they have reached a constant temperature and entropy. At this point, entropy is no longer increasing and the excess thermal energy will dissipate throughout the universe. This process serves as an example of the zeroth law of thermodynamics which states “if two bodies are equal in temperature to a third, they are equal in temperature to each other” (Oakes, 2018, pg. 506).

The first law of thermodynamics states “During a given process, the net heat transfer minus the network output equals the change in energy” (Oakes, 2018, pg. 506). This tells us that energy can convert from (A) to (B). This implies that energy is always being transferred with an increase in disorder (entropy), thus achieved with an increase in heat transfer. If energy is always being transferred, then energy cannot be created or destroyed. Therefore, energy will always exist but without heat-transfer, energy can no longer transfer from one body to another as described in the zeroth law. For example, let’s say we had an insulated system comprising two bodies (A) and (B). Assume the insulation is thick enough to not allow heat to transfer inside and outside of the system. During this example, we will neglect radiation. Then let’s say body (A) has a temperature of 273 Kelvin. This body then comes in physical contact with another body (B) that has a temperature of 293 Kelvin within the isolated system. In this case, the mechanism of heat transfer would be conduction. The heat will transfer from (B) to (A) until they reach a thermodynamic equilibrium of 283 Kelvin. Since the system is being isolated by insulation, once (A) and (B) equalize thermal energy will no longer transfer, thus describing an adiabatic process (Oakes, 2018, pg. 506). The first law also describes the ideal gas law and an isobaric process. Let’s consider the previous example of the boiling water again to describe this process. As the temperature of the stove, pot, and water reach thermodynamic equilibrium the stove stays at a constant temperature, it would be an isothermal process (Oakes, 2018, pg. 506). However, the build-up in pressure becomes relative to the increase in temperature ("Isobaric Process: Thermodynamic Processes"). Let’s say that we expose the pot of water to the surrounding air, in this case, the water molecules will collide at a rapid rate. This will cause the pressure of the water to become constant and thus make it an isobaric process (Oakes, 2018, pg. 506). With the build-up of constant pressure, the molecules will expand to dissipate the kinetic energy ("Isobaric Process: Thermodynamic Processes"). This process is best described by Charles’s law, it states “The volume varies directly with temperature for an ideal gas” (Oakes, 2018, pg. 506). From here we can conclude that the liquid water expands molecules but decreases in volume as it releases the excess temperature by dissipating the volume of the water vapour into the air and thus into the universe ("Isobaric Process: Thermodynamic Processes"). However, what happens when the boiling water is sealed. The volume will remain constant since the water vapour cannot escape from the system. This process describes an isometric (Oakes, 2018, pg. 506). However, when the volume of the water vapour cannot escape the sealed system, the pressure of the thermal energy bombards the walls of the container. The potential energy will constantly increase within the sealed container until the material can no longer sustain the pressure of the molecules colliding and thus the container will explode. The thermal energy then dissipates into the universe.

The second law of thermodynamics states “During a process, the net entropy of the universe cannot decrease” (Oakes, 2018, pg. 506). When considering the real universe, we realize work is exponentially transferring thermal energy by radiation, convection, and conduction throughout the universe. Hence, the universe is exponentially increasing in temperature. Therefore as long as there is work, thermal energy dissipates throughout the universe and will have nowhere to escape. From here we can conclude that the universe will always have an increase of entropy until it reaches a relative maximum thermodynamic equilibrium. As long as work exists in the universe there will be an increase of temperature and thus an increase in entropy. For the universe to reach a thermodynamic equilibrium would imply all forms of potential energy in the universe have transferred to it. At this point work will no longer exist in the universe; thus the entropy can no longer increase, this means the entropy will become constant and the heat will then dissipate throughout the universe until it reaches a state of thermodynamic equilibrium.

The third law of thermodynamics states “The entropy of a system approaches a constant value as the temperature approaches absolute zero” (Kittel & Krömer, 1980). This follows the second law of thermodynamics since the entropy of the universe will never reach a state of thermodynamic equilibrium unless energy is no longer being transferred through work. Therefore, once the maximum thermodynamic equilibrium occurs the universe will equally dissipate its thermal energy until it reaches a value of constant entropy. This only occurs as the temperature of the universe approaches zero Kelvin. However, when one considers the second law of thermodynamics, they will realize that the third law acts as a restriction. If the universe is a closed system, then the system will always have some thermal energy. Therefore, the universe will never reach a temperature of absolute zero unless the thermal energy can escape the system. Then if that’s the case we can further conclude that the thermal energy will just dissipate throughout the universe equalizing at some temperature close to absolute zero. To say that the universe can reach absolute zero would imply the universe is not a closed system and is within another system. As far as I know, this is not the case.

## 1. What is entropy?

Entropy is a measure of the disorder or randomness in a system. In thermodynamics, it is a measure of the amount of energy in a system that is unavailable to do work.

## 2. What are the three laws of thermodynamics?

The first law of thermodynamics states that energy cannot be created or destroyed, only transformed from one form to another. The second law states that the total entropy of a closed system will always increase over time. The third law states that the entropy of a perfect crystal at absolute zero temperature is zero.

## 3. How does entropy relate to the second law of thermodynamics?

The second law of thermodynamics states that the total entropy of a closed system will always increase over time. This means that in any spontaneous process, the total entropy of the universe will increase. Entropy is a measure of the disorder or randomness in a system, so the second law can also be seen as a statement about the tendency of systems to become more disordered over time.

## 4. What is the relationship between entropy and energy?

Entropy is often described as a measure of unavailable energy in a system. This means that as entropy increases, the amount of energy available to do work decreases. Additionally, the second law of thermodynamics states that the total entropy of a closed system will always increase, which means that the amount of available energy will decrease over time.

## 5. Can entropy be reversed?

According to the second law of thermodynamics, the total entropy of a closed system will always increase. This means that while it is theoretically possible to decrease the entropy of a specific system, the total entropy of the universe will still increase due to the energy required to decrease the entropy. Therefore, entropy cannot be reversed on a larger scale.

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