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# Third Law of Thermodynamics

Dive deep into the fascinating world of engineering by exploring the Third Law of Thermodynamics. This theoretical principle, fundamental to the world of physical sciences, significantly impacts modern technology and energy systems. In this discourse, you will gain a thorough understanding of the concept, its discovery, real-world applications, mathematical representation and graphical illustrations. Absorb the vital connection between entropy and the Third Law, and see how it shapes the practical elements of engineering. Master the Third Law of Thermodynamics to enhance your engineering expertise.

## Understanding the Third Law of Thermodynamics

You might ask, what is the Third Law of Thermodynamics? In a simple and straight-forward explanation, it states that the entropy of a perfect crystal of a pure substance approaches zero as the temperature approaches absolute zero.

### The Basic Concept of Third Law of Thermodynamics

To understand this law in depth, let's begin by defining entropy, which is a basic concept at the core of the Third Law of Thermodynamics.

Entropy is a measure of randomness or disorder in a system. In other words, it signifies the degree of energy dispersal in the system.

If we look into a perfect crystal, the atoms within it are perfectly arranged, with no disorder or randomness. Therefore, the entropy or randomness in a perfect crystal is at its minimal level when the temperature is absolute zero (-273.15 Celsius or 0 Kelvin).

A typical example to illustrate this concept could be considering two rooms. The first room is meticulously organized, while the second room is in complete disarray. The first room can be compared to a perfect crystal at absolute zero with low entropy, while the second room represents a system with higher entropy or disorder.

For calculations involving entropy, they are usually conducted using an equation: $\Delta S = \int{\frac{dQ_{rev}}{T}}$ where $$\Delta S$$ is the change in entropy, $$dQ_{rev}$$ is the reversible heat, and $$T$$ is the absolute temperature.

### Who Discovered the Third Law of Thermodynamics?

The Third Law of Thermodynamics was formulated by Walther Nernst, a German chemist and physicist, in the early 20th century. Nernst, who was a Nobel laureate in Chemistry, formulated this law after years of consistent work and research in this field. Some key developments in his research included:
• Investigations on the thermodynamic properties of solutions and solids
• Development of the Nernst heat theorem
• Beginning of the formulation of what we now know as the Third Law of Thermodynamics
Nernst's contributions to the field have significantly shaped the modern understanding of thermodynamics. His work, especially the Third Law, continues to be of profound importance to professionals and enthusiasts in the field of engineering and sciences.

Did you know that besides his work on the Third Law, Nernst is also credited with the development of a theoretical explanation for the observation known as the Nernst effect? This concept, which involves the production of a voltage when a conductor with a temperature gradient is subjected to a perpendicular magnetic field, further manifests his contribution and influence in the field of thermodynamics.

## The Meaning of the Third Law of Thermodynamics

At its foundation, the Third Law of Thermodynamics helps us understand the natural behaviour of materials at extreme temperatures - more specifically, at the hypothetical and unattainable temperature of absolute zero. It predicts that the entropy, which is the measure of randomness or disorder in a system, of a perfect crystal would be zero when the temperature is at absolute zero. This would imply an absolute, perfect order with no randomness or disorder – a state practically impossible to achieve.

### Interpreting the Third Law of Thermodynamics Meaning

Diving deeper into this, imagine an ideal crystal structure. At absolute zero, a perfect crystal has only one possible microscopic arrangement - each atom or molecule is locked into a unique position. Therefore, a perfect crystal has an entropy value of zero at absolute zero, because entropy is associated with the uncertainty or randomness in a system. The Third Law of Thermodynamics also helps explain why absolute zero can't realistically be achieved. As temperature lowers and nears absolute zero, it becomes exponentially difficult to remove heat from a system, requiring infinite steps to exactly reach absolute zero. This links back to the idea that entropy approaches zero as temperature approaches absolute zero while still never able to fully reach it. Scalars often come into play in explanations of thermodynamics. For example, consider the equation: $$\Delta S = \int_{T_i}^{T_f}{\frac{\Delta Q}{T}}$$ This integral from an initial temperature $$T_i$$ to a final temperature $$T_f$$ calculates the absolute entropy change of a system, where $$\Delta Q$$ is the infinitesimal amount of heat added, and $$T$$ the temperature at which it was added.

### Real-World Examples Illustrating the Third Law of Thermodynamics

Let's explore some day-to-day examples that elucidate the Third Law of Thermodynamics. Below are items and situations you'll find around you, which can demonstrate this law quite well:
• Refrigerators and air conditioners: These appliances cool down the enclosed space by removing heat, albeit never reaching absolute zero temperature.
• Liquid nitrogen: Often used to instantaneously freeze foods or medical samples, it offers an idea of how difficult it is to extract heat as the temperature lowers. Even though it has a very low temperature, it isn't at absolute zero.

#### Unpacking Third Law of Thermodynamics Examples

To understand these examples in detail, take the refrigerator. The cooling mechanism involves absorbing heat from the items inside and expelling it outside, lowering the interior temperature. This happens through an evaporation-condensation cycle, employing substances with low boiling points, thus ensuring effective temperature transfer. However, no matter how efficient the refrigerator is, it can never reach a point where the internal temperature becomes absolute zero, even as the externally expelled heat approaches infinity. This proves in a practical real-world scenario, the concept that entropy (the disorder) comes closer to zero as temperature nears absolute zero, but never fully reaches it. In other words, as per the Third Law of Thermodynamics, the thermal motion of particles restricts achieving a perfectly ordered state, reinforcing the link between entropy, temperature, and order in a system.

## Applying the Third Law of Thermodynamics

The Third Law of Thermodynamics isn't reserved for abstract scientific concepts - it's an essential guideline for multiple fields, particularly those related to engineering, chemistry, and physics. It directly influences how chemical reactions, cooling systems, and energy technologies operate.

### Practical Third Law of Thermodynamics Applications

Let's delve into the various real-world scenarios where you'll encounter this incredible law. In fact, you might be surprised how regularly you come into contact with the principles of the Third Law, often without realising it.

To begin, we look at thermal engineering. Systems such as refrigerators and air conditioners are excellent practical examples of the Third Law of Thermodynamics in action. They decrease the internal temperature by expelling heat. Yet, no matter the efficiency or the length of operation time, they can't attain an absolute zero temperature. This is a direct application of the third law - as temperature nears absolute zero, removing further heat from a system becomes increasingly difficult.

Moving to the field of materials science, the Third Law plays a role in determining material properties at different temperatures. Changes in a material's entropy provide insights into its heat capacity, energy storage, or reaction spontaneity, essential in materials design and evaluation.

Chemistry and biochemistry also utilise this law - it aids in predicting reaction outcomes. Since reactions favour directions leading to higher entropy, the law enables the determination of process viability at different temperatures. The Third Law even appears in studies of proteins folding, DNA hybridization, and other biochemical processes.

Finally, quantum computing - a cutting-edge field - is harnessing principles linked to the third law. Qubits, fundamental units of quantum information, function due to low-entropy states, a direct implication of the law. It’s these intricate applications that show just how integrated the third law is in technology and life.

#### Revealing the Entropy Third Law of Thermodynamics Connection

For understanding how the Third Law intricately weaves into these applications, getting to the crux of the "Entropy-Third Law" connection holds immense significance.

To recap, entropy implies the degree of disorder or randomness in a system. The Third Law of Thermodynamics expressly states that the entropy of a perfect crystal at absolute zero is zero.

This posits that as a system nears absolute zero, its entropy theoretically approaches zero as well, signifying an entirely ordered system. Such a perfect state of order can, however, never truly be achieved. It implies that every atom or molecule in the crystal has a precise, unique position, thus eliminating randomness and maximising order.

This 'order' essentially translates to pattern predictability; less entropy indicates a more predictable system. Consequently, designing materials or systems operating close to absolute zero, such as superconductors, or discerning reaction paths, requires a comprehensive understanding of the Third Law and entropy.

Once you comprehend entropy and its nuances, consider the equation below:

$\Delta S = \int_{T_{1}}^{T_{2}} {\frac{Q_{rev}}{T}}$

It relates the changes in entropy ($$\Delta S$$) to a reversible quantity of heat ($$Q_{rev}$$). You can calculate the change in entropy for a process by integrating the quantity of reversible heat over the absolute temperature range from $$T_{1}$$ to $$T_{2}$$.

This formula is fundamental when engineers or physicists tackle problems related to heat transfer, energy conversion, or reactions, drawing the link between the third law, entropy, and practical applications.

In conclusion, tracing the "Entropy-Third Law" connection is a profound aspect of modern science and engineering. It opens windows to understanding and manipulating the microscopic world, creating processes and technologies that shape our everyday experiences.

## The Mathematical Representation of the Third Law of Thermodynamics

The Third Law of Thermodynamics is often optimally expressed in mathematical language. It clarifies concepts and allows the law's applications in numerous scientific and engineering areas. Here, we'll talk about the key equation that encapsulates the Third Law and the constituents of that equation.

### Breaking Down the Third Law of Thermodynamics Formula

The mathematical representation of the Third Law of Thermodynamics is typically seen via the equation of entropy change, as follows:

$\Delta S = \int_{T_{1}}^{T_{2}} {\frac{\Delta Q}{T}}$

In this equation:

• $$\Delta S$$ is the change in entropy
• $$\Delta Q$$ is the infinitesimal amount of heat added or removed
• $$T$$ is the absolute temperature

Let's deconstruct the equation to understand its significance.

Entropy, designated as $$S$$, is the measure of a system's disorder or randomness. The difference between entropy values at two different states (initial and final) is represented as $$\Delta S$$. The greater $$\Delta S$$, the more randomness or disorder introduced into the system. If $$\Delta S$$ is negative, it means the system has become more 'ordered'.

The infinitesimal heat change, denoted by $$\Delta Q$$, represents the tiny increments of heat added to or removed from the system. Combining it with $$T$$, the absolute temperature (measured from absolute zero, not from the Celsius or Fahrenheit scales), gives a measure of how much the introduced heat changes the system's disorder. Dividing $$\Delta Q$$ by $$T$$ downplays the impact of large heat quantities introduced at high temperatures, as these aren't as likely to disorder a system as much.

Integrated together, $$\int_{T_{1}}^{T_{2}} {\frac{\Delta Q}{T}}$$ represents a cumulative sum of changes over a set temperature range, from initial temperature $$T_{1}$$ to final temperature $$T_{2}$$.

### Problem-Solving Using the Third Law of Thermodynamics Formula

With basic knowledge of the Third Law's equation, you are equipped to tackle a variety of problems in physics and chemistry. Let's see how through a step-by-step problem-solving approach:

#### Third Law of Thermodynamics Problem Example

Suppose you're asked to calculate the entropy change when 1 mol of water at 100°C boils to become steam at the same temperature. You're given a latent heat of vaporisation of $$2.26 x 10^6 J mol^{-1}$$.

Here are steps to solve this:

1. Remember $$\Delta S = \int_{T_{1}}^{T_{2}} {\frac{\Delta Q}{T}}$$. Here, as water is boiling, the initial and final temperatures are the same, ie. $$T_{1}= T_{2}= 100°C$$. We convert this to Kelvin (the SI unit) to get $$T = 100 + 273.15 = 373.15 K$$.
2. $$\Delta Q$$ is the heat supplied to transform liquid water into steam, the latent heat of vaporisation. So, $$\Delta Q = 2.26 x 10^6 J mol^{-1}$$.
3. Substitute these into $$\Delta S = \frac{\Delta Q}{T}$$ to get: $\Delta S = \frac{2.26 x 10^6 J mol^{-1}}{373.15 K}$
4. Perform the division to find the entropy change.

Using this equation and approach lets you calculate entropy changes and predict spontaneous reactions, energy efficiency, or even data for creating cooling technologies, underlining the Third Law's indelible mark on practical problem solving.

## Graphics and Visuals on the Third Law of Thermodynamics

Creating a vivid, visual understanding of this law aids in better comprehension and long-term knowledge retention. Through graphics, diagrams, and visual analogies, complex processes and applications related to the Third Law of Thermodynamics can be made more tangible. In the sections that follow, you will get introduced to some of these visual representations and their significance.

### Diagrammatic Representation of Third Law of Thermodynamics Examples

When discussing the Third Law of Thermodynamics, you'll often encounter examples involving perfect crystals and absolute zero temperature. Visualising these concepts can greatly help in understanding the law's implications better.

Consider a perfect crystal. A graphical representation can be a three-dimensional grid with each intersection point showing an atom or a molecule's location. At an absolute zero temperature, each speck on the grid stays at a specific spot, representing the lowest energy state and hence, zero entropy (disorder).

A line graph can be used to illustrate entropy change concerning temperature, which is a direct manifestation of the third law. The graph's x-axis represents the temperature scale from 0 to a given maximum, while the y-axis represents entropy. The line plot starts from the origin (zero entropy at absolute zero) and ascends up and right (entropy increases with temperature). This graph effectively demonstrates the basic tenet of the Third Law - as the temperature of a perfect crystal approaches absolute zero, its entropy approaches zero.

Another worth-mentioning concept is thermodynamic cycles - the Carnot, Stirling, and Ericsson cycles. Here's how these cycles can be represented on a pressure-volume (P-V) or temperature-entropy (T-S) graphs:

• Carnot Cycle: Comprises two isothermal and two adiabatic processes. On the P-V diagram, it forms a rectangle while on the T-S diagram, it forms a trapezoid.
• Stirling and Ericsson Cycles: Stirling encompasses two isothermal and two isochoric processes, whereas Ericsson has two isobaric and two isothermal phases. They create a trapezoidal shape on both the P-V and T-S diagrams, exemplifying how entropy changes.

Visualising these cycles not only helps in understanding changes in energy, work done, and heat exchanges but also aids in grasping how entropy plays a vital role in determining an ideal engine's efficiency.

### Graphics Illustrating Third Law of Thermodynamics Applications

From refrigeration to quantum computing, the Third Law of Thermodynamics finds application in numerous fields. Let's consider three vital areas: thermal engineering, materials science, and quantum computing, and see how graphics can be used to illustrate their interactions with the Third Law.

In thermal engineering, various devices such as a refrigerator or an air conditioner work on the principles of the Third Law. For instance, a flowchart depicting the refrigeration cycle can be created. The flowchart involves four major elements: a compressor, condenser, evaporator, and expansion valve, with arrows to indicate the direction of refrigerant flow. This helps in understanding how these devices can cool down a system but cannot reach absolute zero temperature due to the constraints of the Third Law.

In materials science, the Third Law assists in understanding how properties of materials vary with temperature. A phase diagram, for instance, illustrates different states or phases of a substance under varying temperature and pressure. This graphical representation clearly shows the entropy difference between various states, by indicating the phase boundaries at different pressure-temperature conditions, giving a tangible exemplification of the Third Law in materials properties at their lowest energy state (specifically at absolute zero).

Moving to cutting-edge quantum computing, a Bloch sphere is often used to visualise a qubit, the basic unit of quantum information. The sphere's poles represent the two states of a qubit, and any point inside the sphere symbolises the qubit's state. As a qubit operates under incredibly low entropy conditions, a Bloch sphere indirectly embodies manifestations of the Third Law in quantum computing.

Overall, these graphical representations convey how the Third Law of Thermodynamics is intricately interlinked with various practical applications, creating a tangible connection between abstract principles and real-world phenomena.

## Third Law of Thermodynamics - Key takeaways

• The Third Law of Thermodynamics helps understand the behaviour of materials at extreme temperatures, specifically at absolute zero, predicting that the entropy (a measure of randomness or disorder) of a perfect crystal would be zero. It is the work of Nernst and is integral to the field of engineering and sciences.
• A perfect crystal structure, at absolute zero, has one possible microscopic arrangement with each atom or molecule in a unique position, resulting in zero entropy. This law explains why absolute zero cannot be realistically achieved, as it would require infinite steps to remove heat from a system.
• The Third Law of Thermodynamics' formula for entropy change is $$\Delta S = \int_{T_i}^{T_f}\frac{\Delta Q}{T}$$, where $$\Delta S$$ is the entropy change of a system, $$\Delta Q$$ is the infinitesimal amount of heat added, and $$T$$ is the temperature at which it was added.
• Real-world examples of the Third Law include refrigerators and air conditioners, which never reach absolute zero temperature, and liquid nitrogen, showing the difficulty of extracting heat as temperature lowers.
• The Third Law is not just theoretical but also has practical applications in fields like thermal engineering, materials science, chemistry, biochemistry, and quantum computing. It influences the operation of cooling systems, energy technologies, and can provide insights into material properties, reactions outcomes, and low-entropy states in quantum computing.

#### Flashcards in Third Law of Thermodynamics 15

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What is the third law of thermodynamics?
The Third Law of Thermodynamics states that the entropy of a system approaches a constant value as the temperature approaches absolute zero. This law implies that it is impossible to reach absolute zero temperature in any process.
Who discovered the Third Law of Thermodynamics?
The Third Law of Thermodynamics was discovered by German chemist and physicist Walter Nernst in the early 20th century.
What does the Third Law of Thermodynamics state? Write in UK English.
The Third Law of Thermodynamics states that the entropy of a perfect crystal at absolute zero is exactly equal to zero. This implies that all system processes will cease at absolute zero.
What is a consequence of the third law of thermodynamics?
A consequence of the third law of thermodynamics is that it is impossible to reach absolute zero temperature (0 Kelvin) with any finite number of processes. Absolute zero signifies a state of zero entropy.
What is the application of the third law of thermodynamics?
The Third Law of Thermodynamics is primarily used in the calculation and prediction of thermal properties of substances at absolute zero, such as specific heat capacity, entropy, and enthalpy. It also aids in establishing the absolute entropy of a substance at any temperature.

## Test your knowledge with multiple choice flashcards

What is problem solving based on the Third Law of Thermodynamics formula?

What is the concept of entropy in the context of the Third Law of Thermodynamics?

How is the Third Law of Thermodynamics represented graphically with a perfect crystal and absolute zero temperature?

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