Chemical Thermodynamics

Theory and Applications

W.J. Rankin

• Publisher: CRC Press
• Year: 2019
• Print ISBN: 9780367222475
• eBook ISBN: 9781000704709
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Industrial & Technical Chemistry

This book develops the theory of chemical thermodynamics from first principles, demonstrates its relevance across scientific and engineering disciplines, and shows how thermodynamics can be used as a practical tool for understanding natural phenomena and developing and improving technologies and products.

Concepts such as internal energy, enthalpy, entropy, and Gibbs energy are explained using ideas and experiences familiar to students, and realistic examples are given so the usefulness and pervasiveness of thermodynamics becomes apparent. The worked examples illustrate key ideas and demonstrate important types of calculations, and the problems at the end of chapters are designed to reinforce important concepts and show the broad range of applications. Most can be solved using digitized data from open access databases and a spreadsheet. Answers are provided for the numerical problems.

A particular theme of the book is the calculation of the equilibrium composition of systems, both reactive and non-reactive, and this includes the principles of Gibbs energy minimization. The overall approach leads to the intelligent use of thermodynamic software packages but, while these are discussed and their use demonstrated, they are not the focus of the book, the aim being to provide the necessary foundations. Another unique aspect is the inclusion of three applications chapters: heat and energy aspects of processing; the thermodynamics of metal production and recycling; and applications of electrochemistry.

This book is aimed primarily at students of chemistry, chemical engineering, applied science, materials science, and metallurgy, though it will be also useful for students undertaking courses in geology and environmental science.

A solutions manual is available for instructors.

1 An overview of thermodynamics

A theory is the more impressive the greater the simplicity of its premises is, the more different kinds of things it relates, and the more extended is its area of applicability. Therefore the deep impression which classical thermodynamics made upon me. It is the only physical theory of universal content concerning which I am convinced that within the framework of the applicability of its basic concepts, it will never be overthrown.

Albert Einstein^*

* A. Einstein, Autobiographical Notes, in Schilpp, P. A. 1949. Albert Einstein: Philosopher–Scientist, New York: Tudor Publishing Company, p. 33.

Scope

This chapter provides a brief historical introduction to the discipline of thermodynamics and a qualitative introduction to the laws of thermodynamics.

Learning objectives

1. Gain an appreciation of the historical context of thermodynamics and its development, particularly the branch known as chemical thermodynamics.
2. Understand, qualitatively, the concepts of internal energy, enthalpy, entropy and Gibbs energy.
3. Gain a simple understanding of the four laws of thermodynamics.

1.1 What is thermodynamics?

In broad terms thermodynamics is the study of the behaviour of matter in an environment where it loses or gains energy. How our understanding of this has developed has been a long and often circuitous process. The physical behaviour of matter was well understood by the beginning of the 19th century, due in great measure to the pioneering work of Isaac Newton, and it was known that it can be described in terms of its motion (its kinetic energy) and position (its potential energy). However, it was also understood that its behaviour could be influenced by other factors such as heat and pressure. The realisation that kinetic and potential energy, heat and pressure could be converted from one form to another was a major advance in understanding which ultimately led to the development of a general description of the behaviour of matter. It also led to the development of steam and other heat engines in which thermal energy is converted to mechanical energy.

Thus, as originally conceived, thermodynamics was the study of the relationship between heat (and the related concept of temperature), energy and work. This is reflected in the name: Thermo (meaning heat) and dynamics (meaning motion). However, as understanding developed, the discipline of thermodynamics expanded to encompass all the influences that affect the behaviour of matter – chemical, electrical and magnetic effects, in addition to mechanical and thermal.

The discipline of thermodynamics is relevant to all branches of science and engineering because it enables us to determine whether a process or change of interest is feasible and, if it is feasible, the maximum energy that can be obtained from the process or, if the process is not feasible, the minimum energy required to make it occur. This is true whether the process belongs to the realm of physics, chemistry, biology, geology, astrophysics or any other branch of science. Accordingly, thermodynamics has great explanatory power and is useful in developing understanding of existing processes and phenomena, both natural and artificial. Equally importantly, it has great predictive capabilities which are useful in developing new materials, processes and products and improving existing materials, processes and products. It has practical application in fields such as the development and application of materials, energy production, storage and consumption, geochemistry, the chemical and metallurgical industries and the environment.

1.2 A brief history

The beginnings of thermodynamics as a scientific discipline can be traced back almost 400 years. In 1650, in Magdeburg in modern day Germany, Otto von Guericke, a natural philosopher and politician, designed and built a pump and demonstrated that a vacuum can exist, thereby disproving Aristotle’s long-held assertion that a vacuum is physically impossible to achieve – ‘nature abhors a vacuum’. In England, the physicist and chemist Robert Boyle read of Guericke’s designs and, in 1656 with scientist Robert Hooke, built a vacuum (or air) pump. Using this pump, Boyle and Hooke discovered the correlation between pressure and volume now known as Boyle’s law.

In 1679, Denis Papin who was collaborating with Boyle built a steam digester, an early form of pressure cooker consisting of a closed vessel with a tightly fitting lid that confined the steam to create a high pressure. His designs included a pressure release valve that kept the vessel from accidentally exploding. By watching the valve move rhythmically up and down to maintain a constant pressure in the vessel, Papin conceived the idea of using a piston moving backwards and forwards in a cylinder as the basis of a steam-driven engine. After moving to Marburg (in Germany), Papin built the first piston steam engine in 1690. This relied on creating a partial vacuum in a vessel by condensing steam, then allowing atmospheric pressure to drive water into the vessel. In 1697 Thomas Savery built a steam-operated water pump based on Papin’s designs. In 1695 Papin moved to Kassel (also in Germany) where, in 1705, he developed a second steam engine with the help of Gottfried Leibniz, based on Savery’s design but utilising steam pressure rather than atmospheric pressure. Details of the engine were published in 1707.

Around 1712 in England, Thomas Newcomen, an ironmonger by trade, combined the ideas of Savery and Papin to make the first practical steam engine.^* He replaced Savery’s receiving vessel (in which the steam was condensed) with a cylinder containing a piston. Instead of the vacuum drawing in water, it drew down the piston. This was used to rock a large wooden beam supported on a central fulcrum. On the other side of the beam was a chain attached to a pump located at the bottom of a mine so that water could be removed from the mine. In each cycle, the cylinder was filled with steam as the piston was pushed outwards; then a small amount of water was injected into the cylinder to condense the steam and create a low pressure, allowing the piston to move back inwards.

* An animation showing the operation of Newcomen’s engine can be found at: https://en.wikipedia.org/wiki/Thomas_Newcomen

The concepts of heat capacity (or specific heat) and latent heat, necessary for the development of thermodynamics, were developed around 1761 by Joseph Black, a professor at the University of Glasgow. James Watt was employed as an instrument maker at the university where he met Black who encouraged him to improve the efficiency of Newcomen’s steam engine. While working from time-to-time over the period 1763 to 1775, Watt conceived the idea of a condenser located external to the cylinder. In this way, steam could be condensed without cooling the piston and cylinder walls as did the internal spray in Newcomen’s engine. The efficiency of Watt’s engine was more than double that of the Newcomen engine. Watt’s engine was commercialised in 1776 and became one of the major driving forces of the industrial revolution, making possible the replacement of water power by steam power.

Drawing on previous work, in 1824 Sadi Carnot, a French military engineer and physicist, published the book Reflections on the Motive Power of Fire which outlined the basic energy relations between heat engines and motive power. It anticipated the second law of thermodynamics and marked the start of thermodynamics as a modern science. In 1843 James Joule, an English physicist from a wealthy brewing family, published a paper Mechanical Equivalent of Heat which anticipated the first law of thermodynamics. The first and second laws of thermodynamics emerged in a formal sense in the 1850s primarily out of the works of William Rankine (a professor of civil and mechanical engineering at the University of Glasgow), Rudolf Clausius (a German physicist) and William Thomson (later Lord Kelvin). The first textbook of thermodynamics, published in 1859, was written by William Rankine.

Thus, by the middle of the 19th century, the nature of energy was well understood. Its transformations from one form to another had been well studied, and both the principle of its conservation (the first law of thermodynamics) and the basis for determining the direction of energy-driven changes (the second law) had been established. All of this knowledge had been derived largely from the desire to improve the efficiency of steam engines. Thermodynamics was thus founded on the basis of turning heat from burning fuel into work in the form of mechanical motion.

In 1865, Rudolf Clausius suggested that the principles of thermodynamics could be applied to chemical reactions. However, it was mainly through the work of the American mathematical physicist Josiah Willard Gibbs, a professor at Yale College (now Yale University), that it became clear that the principles developed for steam power applied equally well in other situations. Between 1873 and 1876 Gibbs published a series of three papers, the most famous being On the Equilibrium of Heterogeneous Substances. In these papers, Gibbs built on the work of Clausius and showed, through graphical and mathematical means, how the first and second laws of thermodynamics could be used to determine the thermodynamic equilibrium of chemical processes as well as their tendencies to occur. However, the significance of Gibbs’ work was not fully appreciated for several more decades.

In the early decades of the 20th century, two major books were written which showed how the principles developed by Gibbs could be applied to chemical processes. These books established the foundation of the science of chemical thermodynamics: Thermodynamics and the Free Energy of Chemical Substances by Gilbert N. Lewis and Merle Randall (at the University of California, Berkeley), published in 1923, and Modern Thermodynamics by the Methods of Willard Gibbs by Edward A. Guggenheim (at the University of Reading), published in 1933. Lewis, Randall and Guggenheim are considered the founders of modern chemical thermodynamics because of the major contribution of their books in unifying the application of thermodynamics to chemistry.

1.3 The laws of thermodynamics

The discipline of thermodynamics is based on four laws, the laws of thermodynamics. These are simple, universal statements of conclusions drawn from observations and measurements of phenomena that occur on Earth and throughout the universe; that is, they are empirical laws based on observations and experimental results produced over time and across all areas of science and found to be repeatable and internally consistent.

The zeroth law. The zeroth law of thermodynamics is concerned with the relationship between temperature and heat flow. It states that if two systems are each in thermal equilibrium with a third, then all three are in thermal equilibrium with each other.

The first law. The first law of thermodynamics deals with the conversion of thermal energy into other forms of energy, enabling us to calculate how much heat may be obtained from, or is required to carry out, a given process. In its simplest form, the first law states that the total energy of an isolated system^* is constant; energy can be transformed from one form to another but cannot be created or destroyed.

* An isolated system is one that has a boundary that prevents the transfer of both matter and energy; no matter or energy is exchanged with its surroundings.

The second law. The second law of thermodynamics tells about the direction in which natural processes occur and allows answers to questions such as:

• Will a system change from State 1 to State 2 under given conditions? If not, how can the conditions be altered in order to make the change occur?
• Under what conditions will the system change from State 1 to State 2 spontaneously, that is, without any external help?

The second law deals only with the feasibility of change, not with the rate of change. The study of rate of change (kinetics) is not the domain of thermodynamics.

The third law. The third law of thermodynamics states that there is an absolute zero of temperature (−273.15°C), though in practice it can never be achieved. At this temperature, systems have their greatest order at the molecular level. The third law is used in the evaluation of a quantity called entropy.

These four laws lead directly to the definition of a number of important thermodynamic quantities, as briefly discussed below.

From the first...

Table of contents

• Cover
• Half-Title
• Title
• Copyright
• Contents
• Preface
• A note to students
• Author
• Units
• Nomenclature
• Constants
• Chapter 1 An overview of thermodynamics
• Chapter 2 Fundamental concepts
• Chapter 3 Gases
• Chapter 4 The first law
• Chapter 5 Sources of thermodynamic data for substances
• Chapter 6 Some applications of the first law
• Chapter 7 The second and third laws
• Chapter 8 Gibbs and Helmholtz energies
• Chapter 9 Solutions
• Chapter 10 Reactive systems – single reactions
• Chapter 11 Gibbs energy applications to metal production
• Chapter 12 Electrolyte solutions
• Chapter 13 Phase equilibria: non-reactive systems
• Chapter 14 Phase equilibria: reactive systems
• Chapter 15 Complex equilibria
• Chapter 16 Electrochemistry
• Chapter 17 Some applications of electrochemistry
• Answers to problems
• Index