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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 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

Response to conditions  

This chapter addresses a very important question in chemistry, which is how to influence the yield of a reaction by increasing the equilibrium constant by changing the conditions, especially the temperature, at which the reaction takes place. Le Chatelier's principle states that when a system at equilibrium is subjected to a disturbance, the composition of the system adjusts so as to tend to minimize the effect of the disturbance. The variation of an equilibrium constant with temperature is expressed by the van 't Hoff equation. The chapter then differentiates between an endothermic reaction and an exothermic reaction. When a system at equilibrium is compressed, the composition of a gas-phase equilibrium adjusts so as to reduce the number of molecules in the gas phase. Meanwhile, the equilibrium constant of a reaction is independent of the presence of a catalyst and is independent of the pressure.

Chapter

Cover Elements of Physical Chemistry

Heat  

This chapter focuses on heat, which, together with work, plays a central role in the formulation of thermodynamics. ‘Heating’ is the process of transferring energy as a result of a temperature difference between the system and its surroundings. It may occur by conduction, when the system is in direct thermal contact with the surroundings, or by radiation, when energy is transmitted as electromagnetic radiation. Walls that permit heating as a mode of transfer of energy are called diathermic, while walls that do not permit heating even though there is a difference in temperature are called adiabatic. The chapter then differentiates between an exothermic process and an endothermic process, before considering heat capacity, calorimetry, and heat influx during expansion.

Chapter

Cover Chemistry for the Biosciences

Energy: what makes reactions go?  

This chapter explores the nature of energy, looking at how energy transfer drives the biochemical processes on which organisms depend for life. Energy is the capacity something has to do work, and is transferred between a system and its surroundings in the form of work and heat. The chapter introduces the concepts of enthalpy and entropy, and explains how the energy change associated with a chemical reaction is called the enthalpy change of reaction. Meanwhile, entropy is a measure of the energetic disorder of a system. The chapter also considers spontaneous reactions and what determines their spontaneity, and introduces the concept of Gibbs free energy.

Chapter

Cover Non-Aqueous Solvents

General properties  

This chapter focuses on the importance of non-aqueous liquids in living systems, and states that water is considered the most abundant liquid on earth. It examines the range of liquid solvents available and discusses how the choice of solvents is related to the various solvent properties. It also explains that solvents are used to bring reactants together at suitable concentrations, such as endothermic reactions wherein heat can be supplied readily by heating the solvent and exothermic reactions wherein the solvent can act as a heat sink. The chapter discusses how solvents frequently react with solutes and how solutions offer a convenient way of delivering chemical compounds to their point of use. It outlines the multiple types of solvent that act as a solvent to different solutes.

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 Chemical Reaction Engineering

The energy balance and temperature effects  

This chapter demonstrates how reactors need not be isothermal. It looks at how reaction rate depends upon temperature for different classes of reaction, including irreversible reactions, reversible endothermic reactions, and reversible exothermic reactions. The chapter then formulates the energy balance for given reactors and uses this to investigate the variation of temperature and therefore reaction rate with time or position in the reactor. This, in turn, can be used to calculate reactor volumes and residence times for a given duty. The chapter also considers steady-state multiplicity in continuous stirred tank reactors (CSTRs) and multistage adiabatic plug flow reactor (PFR). For a PFR, there exists an optimum temperature profile or line of maximum reaction rate and it is important to try to approach this path. The chapter discusses two different methods for achieving this: interstage cooling and cold-shot cooling.