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Chapter

Cover Physical Chemistry for the Life Sciences

Entropy  

This chapter shows how the entropy of an isolated system increases in a spontaneous process. The concept of entropy lies behind the reason why any chemical or physical process has a tendency to occur. It is therefore central to understanding the web of chemical processes that take place in living organisms. To that end, the chapter discusses the direction of spontaneous change and how to identify the reason why some processes are spontaneous and others are not. Next, the chapter explains the relationship between entropy and the Second Law of thermodynamics, which states that ‘the entropy of an isolated system tends to increase’. Absolute entropies and the Third Law of thermodynamics are also considered.

Chapter

Cover Why chemical reactions happen

Equilibrium  

This chapter covers equilibrium. It starts with the concept of the Second Law of Thermodynamics and Gibbs energy impacting entropy. It notes the general chemical equilibrium in terms of gas, solid, liquid, and solution. The chapter uses diagrams and equations to show how equilibrium is achieved in relation to Gibbs energy and equilibrium constants. It investigates how temperature, dimerization, extraction of metals, concentration, the Haber process, and coupling reactions influence the position of equilibrium. Additionally the chapter explores the rates of reaction in terms of equilibrium.

Chapter

Cover Chemical Structure and Reactivity

Thermodynamics and the Second Law  

This chapter assesses how the approach to chemical equilibrium is governed by the Second Law of Thermodynamics, which involves the physical property known as entropy. These ideas arise within the physical theory generally known as thermodynamics. Thermodynamics is a theory which describes the behaviour of bulk matter; quantum mechanics, in contrast, focuses on the behaviour of individual atoms and molecules. Of course, it is certainly the case that the behaviour of a mole of hydrogen molecules must be intimately connected to the properties of a single hydrogen molecule, and this connection can be made in a precise way using statistical thermodynamics. However, the principles of thermodynamics are not dependent on an understanding of the microscopic behaviour of atoms and molecules. The chapter also looks at spontaneous processes and the Gibbs energy.

Chapter

Cover Elements of Physical Chemistry

Entropy  

This chapter begins by defining spontaneous change, which is a change that has a tendency to occur without work having to be done to bring it about. The apparent driving force of spontaneous change is the tendency of energy to disperse and matter to become disordered. The measure of dispersal used in thermodynamics is called entropy. When matter and energy become dispersed, entropy increases. That being so, the basic principle underlying change can be expressed as the second law of thermodynamics: entropy of an isolated system tends to increase. The tendency of energy to disperse explains the fact that, despite numerous attempts, it has proved impossible to construct an engine in which heat, perhaps from the combustion of a fuel, is drawn from a hot reservoir and completely converted into work, such as the work of moving an automobile.

Book

Cover Elements of Physical Chemistry

Peter Atkins, Julio de Paula, and David Smith

Elements of Physical Chemistry begins with an examination of the properties of gases. It then looks at the first law of thermodynamics and the second law of thermodynamics. Next it moves on to physical transformations, chemical change, chemical kinetics, and quantum theory. There are also chapters on atomic structure, the chemical bond, molecular interactions, molecular spectroscopy, and statistical thermodynamics. Other topics include magnetic resonance, macromolecules and aggregates, and solids.

Chapter

Cover Making the Transition to University Chemistry

Spontaneous Change, Entropy, and Gibbs Energy  

This chapter explores the concepts of spontaneous change, entropy, and Gibbs energy. Whilst spontaneous changes have a natural tendency to occur, the Gibbs energy equation cannot be used to predict the reaction rate. Entropy is a measure of the dispersal of energy. The criterion for spontaneous change is mostly based on the Second Law of thermodynamics. Gibbs energy, additionally, is the combination of enthalpy and entropy together to form a single physical quantity. An Ellingham diagram includes graphs showing the Gibbs energy change of formation for various metal oxides as a function of temperature. Finally, the chapter looks into the possibilities of negligible entropy changes or enthalpy changes in the systems.

Chapter

Cover Why chemical reactions happen

What this book is about and who should read it  

This chapter introduces the concept of chemical reactions. It mentions how the Second Law of Thermodynamics does not really help explain the science behind chemical reactions in detail. The chapter lists the interactions which lead to the formation of chemical bonds: electrostatic interactions and covalent interactions. Moreover, it previews the topics to be discussed in latter chapters. The chapter describes the people who would benefit from reading the book, such as university students and teachers. It notes the abbreviations and systematic names for compounds that will also be used across the title.

Chapter

Cover Why chemical reactions happen

What makes a reaction go?  

This chapter looks into the process of a reaction. It explains the equations used to derive changes to chemical reactions. The chapter explores energy changes by referencing how temperature plays a big role in line with endothermic, exothermic, entropy, and the Second Law of Thermodynamics. It discusses the chemical process of generating ice. Energy change is due to the making and breaking of chemical bonds alongside their links to a reaction. In addition, the chapter uses Gibbs energy to compute the entropy change of systems in terms of quantity. It highlights the significance of achieving equilibrium in terms of reactions.

Chapter

Cover Elements of Physical Chemistry

The Gibbs energy  

This chapter looks at Gibbs energy, which is a central concept in chemical thermodynamics and electrochemistry. It begins by looking at the standard reaction entropy, which is the difference in molar entropy between the products and the reactants in their standard states. To apply the second law correctly, it is important to calculate the total entropy, the sum of the changes in the system and the surroundings that jointly compose the ‘isolated system’ referred to in the second law. Provided the temperature and pressure are constant, the direction of spontaneous change is in the direction of decreasing Gibbs energy. At constant temperature and pressure, the maximum non-expansion work available from a process is equal to the change in Gibbs energy.

Chapter

Cover Animal Physiology

Energy Metabolism  

This chapter discusses energy metabolism. It defines energy metabolism as the sum of the processes by which animals acquire energy, channel energy into useful functions, and dissipate energy from their bodies. Energy metabolism consists of two subsets: catabolic processes and anabolic processes. Animals utilise their absorbed chemical energy for biosynthesis, maintenance, and generation of external work. The chapter then correlates the second law of thermodynamics to the reason why animals require energy. It discusses metabolic rate as the rate at which an animal consumes energy before detailing the factors that affect metabolic rates, such as gender and time of day.

Chapter

Cover Atkins’ Physical Chemistry

The measurement of entropy  

This chapter studies the measurement of the entropy of a substance, which is important to make the Second Law quantitative. This is achieved by measuring heat capacities. The chapter then looks at the calorimetric measurement of entropy. Entropies are determined calorimetrically by measuring the heat capacity of a substance from low temperatures up to the temperature of interest and taking into account any phase transitions in that range. The chapter also explains the Debye extrapolation, the Nernst heat theorem, and the Third Law of thermodynamics. Finally, it considers the standard reaction entropy, which is the difference between the molar entropies of the pure, separated products and the pure, separated reactants, all substances being in their standard states.

Chapter

Cover Atkins’ Physical Chemistry

Entropy  

This chapter explores the property called ‘entropy’, which is central to the formulation of the ‘Second Law of thermodynamics’. Entropy is the concept on which almost all applications of thermodynamics in chemistry are based: it explains why some physical transformations and chemical reactions are spontaneous and others are not. A change in entropy is defined in terms of reversible heat transactions. The Carnot cycle is used to prove that entropy is a state function. Meanwhile, the efficiency of a heat engine is the basis of the definition of the thermodynamic temperature scale and one realization of such a scale, the Kelvin scale. The chapter then looks at the Clausius inequality, which is used to show that the entropy of an isolated system increases in a spontaneous change and therefore that the Clausius definition is consistent with the Second Law.