Posted on Categories:Thermodynamics, 热力学, 物理代写

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## 物理代写|热力学代写Thermodynamics代考|Why Does Entropy Seem So Complicated?

Students and authors alike dread the subject of entropy. To be sure, entropy, denoted ‘ $S$ ‘, is a state function like no other. Equally clear is that it is of central importance to thermodynamics – being intimately associated with two of the four Laws. Yet many individuals – even science professionals who use entropy every day – wrestle with the basic question of what it actually is, exactly.

It is an interesting exercise to review how the different authors address this question. Among the reference textbooks, entropy-or its explanation – has been described (sometimes apologetically!) as follows: “mysterious;” “uncomfortable;” “the most misunderstood property of matter;” “less than satisfying;” “less than rigorous;” “confused;” “rather abstract;” “rather subjective;” “difficult to fully comprehend…physical implications that are hard to grasp;” “not a household word, like energy;” etc. Perhaps Cengel puts it most poignantly and directly:

This does not mean that we know entropy well, because we do not. In fact, we cannot even give an adequate answer to the question, “what is entropy?”
It does not have to be this way.
First and foremost, entropy is a quantity. This means that any description of entropy that purports to be a definition had better have a number attached to it. Moreover, the physical meaning of that number should be clear-e.g., we must know precisely what it means to “add one” to it, in the same way that we know precisely what it means to add one calorie of heat to a gram of water.

## 物理代写|热力学代写Thermodynamics代考|Entropy as Unknown Molecular Information

Without further ado, here is a qualitative version of the information definition of entropy:

Definition 10.1 (qualitative) Entropy is the amount of molecular information that a macroscopic observer does not know about the system.

Recall from Section $3.1$ that thermodynamics provides a complete description of reality at the macroscopic scale only; at the molecular scale, it is largely incomplete. Thus, precise knowledge of the thermodynamic state of the system [e.g., of the thermodynamic variables $(T, V)$ ] tells us very little about the molecular state. The details of the latter-i.e., positions, velocities, and internal states of every constituent molecule – must therefore be considered information that is mostly unknown to a macroscopic observer. According to Definition 10.1, the amount of this missing molecular information is the entropy.

## MATLAB代写

MATLAB 是一种用于技术计算的高性能语言。它将计算、可视化和编程集成在一个易于使用的环境中，其中问题和解决方案以熟悉的数学符号表示。典型用途包括：数学和计算算法开发建模、仿真和原型制作数据分析、探索和可视化科学和工程图形应用程序开发，包括图形用户界面构建MATLAB 是一个交互式系统，其基本数据元素是一个不需要维度的数组。这使您可以解决许多技术计算问题，尤其是那些具有矩阵和向量公式的问题，而只需用 C 或 Fortran 等标量非交互式语言编写程序所需的时间的一小部分。MATLAB 名称代表矩阵实验室。MATLAB 最初的编写目的是提供对由 LINPACK 和 EISPACK 项目开发的矩阵软件的轻松访问，这两个项目共同代表了矩阵计算软件的最新技术。MATLAB 经过多年的发展，得到了许多用户的投入。在大学环境中，它是数学、工程和科学入门和高级课程的标准教学工具。在工业领域，MATLAB 是高效研究、开发和分析的首选工具。MATLAB 具有一系列称为工具箱的特定于应用程序的解决方案。对于大多数 MATLAB 用户来说非常重要，工具箱允许您学习应用专业技术。工具箱是 MATLAB 函数（M 文件）的综合集合，可扩展 MATLAB 环境以解决特定类别的问题。可用工具箱的领域包括信号处理、控制系统、神经网络、模糊逻辑、小波、仿真等。