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Chapter

Cover Making the Transition to University Chemistry

Thermochemistry  

This chapter focuses on thermochemistry. It starts with enthalpy change which is the heat added to a system at constant pressure. The reaction is considered endothermic if heat is taken, while it would be exothermic if heat is given out. As the chapter shows, a calorimeter can be used to measure enthalpy changes. According to Hess's law, the standard enthalpy change for a reaction is independent of the route taken from reactants to products. Atomization enthalpy, on the other hand, is the standard enthalpy change accompanying the formation of a gaseous atom from either a solid or a gas containing molecule. Finally, the chapter explains bond enthalpy, solution enthalpy, and hydration enthalpy as well.

Chapter

Cover Chemistry3

p-Block chemistry  

This chapter describes p-block elements as those with the valence electron configuration ns2 npx , where x is between 1 and 6. Some elements of the p-block have properties that are intermediate between those of metals and non-metals, and these elements are often called metalloids. The chapter explains trends in behaviour across the periods and down the groups of the p-block and confirms why the metal/non-metal divide runs diagonally through the p-block. It illustrates how to use enthalpy cycles together with bond enthalpies to determine the differences in stabilities of compounds going down a group. The structures and key reactions of the p-block oxides, hydroxides, oxoacids, and halides are also covered.

Chapter

Cover Elements of Physical Chemistry

Chemical change  

This chapter explores thermochemistry, one of the principal applications of thermodynamics to chemistry. It begins by looking at how the strengths of bond are expressed in terms of the bond dissociation enthalpy and their mean values over a series of related compounds. The chapter then considers the standard enthalpy of combustion, which is the change in standard enthalpy per mole of combustible substance. Meanwhile, the reaction enthalpy is the change in enthalpy that accompanies a chemical reaction. The standard reaction enthalpy (the ‘standard enthalpy of reaction’) is the value of the reaction enthalpy when all the reactants and products are in their standard states. The chapter also discusses Hess's law, the standard enthalpy of formation, exothermic and endothermic compounds, and Kirchhoff's law.

Chapter

Cover Foundations of Physical Chemistry: Worked Examples

Chemical energetics  

This chapter includes problems and answers that illustrate Hess's law, enthalpies of formation, bond enthalpies, lattice energies, and the stability of solids. It discusses enthalpy and entropy changes that accompany reactions, and reviews the prediction of direction of chemical change via free energy changes. It also introduces the temperature variation of enthalpy changes and heat changes at constant pressure as compared to constant volume. The chapter highlights the second law of thermodynamics and the prediction of the direction of chemical changes, including the Ellingham diagrams and the Born-Landé equation for the prediction of lattice energies. It emphasizes that the standard enthalpy of formation of a compound is the enthalpy change involved in the formation of one mole of the substance from its elements.

Chapter

Cover Physical Chemistry for the Life Sciences

Fundamental processes  

This chapter covers a widely used approach in thermodynamics — breaking down the process of interest into a series of simpler steps. The enthalpy change associated with the overall process is then equal to the sum of the changes for the individual steps. Commonly occurring steps include phase transitions, ionization and electron gain, and bond dissociation and formation. Phase transitions include freezing, melting, vaporizing, and their analogues in membranes. Ionization is the process of losing one or more electrons and electron gain is the opposite. Bond dissociation and bond formation are fundamental steps in many chemical reactions, and are essential components in the analysis of the overall enthalpy change accompanying a biochemically significant reaction. To describe these processes quantitatively, the chapter discusses the necessity of specifying the conditions, such as the pressure and temperature, under which they take place.

Chapter

Cover Inorganic Chemistry

Molecular structure and bonding  

This chapter examines the development of models of molecular structure in terms of the concepts of valence bond and molecular orbital theory. It reviews the methods for predicting the shapes of molecules. The discussion covers the Lewis structures, octet rule, and VSEPR model. The chapter introduces the concepts of bond order and correlations. Then, it looks at bond length, bond strength, and reaction enthalpies. Lastly, it explains the basic principles of catalysis, discussing energetics, catalytic cycles, catalytic efficiency and lifetime, selective catalysts, as well as homogeneous and heterogeneous catalysts. The chapter illustrates the importance of the interplay between qualitative models, experiments, and calculations.

Chapter

Cover Inorganic Chemistry

Periodic trends  

This chapter discusses trends in the physical and chemical properties of the elements. It emphasizes that understanding periodicity—the regular manner in which the physical and chemical properties of the elements vary with atomic numbers–is vital in the chemistry of the elements and their compounds. The chapter takes a closer look at valence electron configurations, atomic parameters, occurrence, metallic character, and oxidation states. In examining the periodic characteristics of compounds, the chapter also discusses the presence of unpaired electrons, coordination numbers, bond enthalpy trends, and binary compounds. Lastly, it tackles the wider aspects of periodicity and the anomalous nature of the first member of each group.

Chapter

Cover Chemical Structure and Reactivity

Bonding in solids  

This chapter focuses on bonding in solids, particularly metallic bonding. In solids, the overlap between orbitals on different atoms can give rise to crystal orbitals which extend throughout the material; these orbitals are analogous to delocalized molecular orbitals. The crystal orbitals which arise from a particular set of atomic orbitals form a band, which can hold a certain number of electrons. The electrical conductivity of metals is the result of partially filled bands; insulators have full bands, but in semiconductors there is a small gap between a filled and an empty band. The lattice enthalpy of an ionic solid can be estimated using a simple electrostatic model. It depends on the size (radii) of the ions and their three-dimensional arrangement in the crystal.

Chapter

Cover Making the Transition to University Chemistry

Halogenoalkanes  

This chapter explains the concept of halogenoalkanes which have carbon-halogen bonds which are significantly polar. However, the carbon atom is partially positively charged and susceptible to a nucleophilic attack. The chapter explains that carbon-halogen bond enthalpy determines the relative rate of reaction. The three common nucleophilic substitution reactions of halogenoalkanes involve sodium hydroxide, potassium cyanide, and ammonia. Elimination is the second vital characteristic type of reaction of halogenoalkanes as it produces an alkene. The hydroxide ion is acting as the base of the compound rather than a nucleophile. Elimination is favoured over substitution where we see nucleophiles with strong bases, bulky nucleophiles, and high temperatures.