This chapter describes how the extension of the concept of chemical potential to
real solutions involves introducing an effective concentration called an ‘activity’.
In certain cases, the activity may be interpreted in terms of intermolecular
interactions; an important example is a solution containing ions. Such solutions
often deviate considerably from ideal behaviour on account of the strong, long-range
interactions between the charged species. The chapter shows how a model can be used
to estimate the deviations from ideal behaviour when the solution is very dilute,
and how to extend the resulting expressions to more concentrated solutions. It looks
at the Margules equations, the Debye–Hückel theory, and the Debye–Hückel limiting
law.
Chapter
Activities
Chapter
Ratio and Proportion
This chapter focuses on the expression and comparison of ratio and proportion. The ideas of ratio and proportion can be expressed using a variety of symbols. Their notation is often used interchangeably when describing these ideas. A part-to-whole ratio is often expressed as a fraction, especially since a diagram can be a helpful way to visualise ratio. The chapter also considers the notions of probability and the term concentration in relation to the notion that solutions can be expressed as the mass of a substance per volume. It then considers the dilution of a solution which is carried out to make the concentration ten times less.
Chapter
Chemical kinetics
This chapter explores how rate laws are determined. This will involve looking at experimental methods, as well as at how the form of the rate law can be determined from data of concentration as a function of time. Concentration can be measured as a function of time by using various physical methods such as the measurement of absorbance, conductance, or pressure. The chapter then looks at two fundamental theories about the rates of reactions: collision theory, which is based on gas kinetic theory, and the more sophisticated transition state theory. Gas kinetic theory can be used to estimate the collision rate and hence the rate constant; however, in its simplest form, the theory massively overestimates the rate constant. Reactions can be thought of as taking place on a potential energy surface.
Chapter
Kinetics
This chapter discusses rates of reactions in kinetics. The rate of reaction is based on the rate of change of concentration per unit time. The activation energy for a reaction is the minimum energy necessary for a collision to lead to a successful reaction. The rate of reaction, then, depends on the concentration of the reactants, temperature, presence of a catalyst, and state of subdivision. The Maxwell–Boltzmann distribution pins the number of molecules in a gas with given energy against energy. On the other hand, the Arrhenius equation measures the activation energy on how the rate constant depends on the temperature.
Chapter
Chemical Equilibrium
This chapter introduces equilibria and equilibrium constants. Equilibrium is recorded when the rate of the forward reaction equates to the rate of the backwards reaction. When equilibrium has been reached, the concentrations of all the substances remain constant. The thermodynamic equilibrium constant is devised when the standard Gibbs energy change is in line with the natural logarithm of the equilibrium constant. The chapter lists the equilibrium calculations mostly used in universities. Le Chatelier's principle refers to the small conditions changes subjected at a system in equilibrium as the equilibrium tends to shift to minimize the effect of the change.
Chapter
Ratio and Proportion
This chapter focuses on the expression and comparison of ratio and proportion. The ideas of ratio and proportion can be expressed using a variety of symbols. Their notation is often used interchangeably when describing these ideas. A part-to-whole ratio is often expressed as a fraction, especially since a diagram can be a helpful way to visualise ratio. The chapter also considers the notions of probability and the term concentration in relation to the notion that solutions can be expressed as the mass of a substance per volume. It then considers the dilution of a solution which is carried out to make the concentration ten times less.
Chapter
Moles, concentrations, and dilutions: making sense of chemical numbers
This chapter details the language of measuring chemical quantities, focusing on one quantity in particular: the mole. The mole is a convenient way of scaling down large numbers: one mole of atoms represents 6 × 1023 atoms. The molar mass is the mass of one mole of a substance. The concentration of a solution tells us how much of a substance is present in a particular volume of that solution. When preparing solutions according to percentage by weight, one uses a mass of substance that equates to a certain percentage of the volume of the final solution. The chapter then looks at dilutions, explaining how the number of moles of the solute remain the same after dilution, but the total volume increases, so the concentration decreases. The chapter also highlights some of the tools for measuring concentrations, including titrations, UV-visible spectroscopy, atomic emission spectroscopy, and fluorescence spectroscopy.
Chapter
Competing reactions in homogeneous systems
This chapter focuses on competing reactions in homogeneous systems. In process development, a good yield is often key to obtaining satisfactory material costs, purity, and robust operation. The essence of obtaining a good chemical yield is the understanding and control of those processes which compete with the desired reaction. This understanding is necessary to obtain a satisfactory laboratory process and, even more so, to scale-up the process for manufacture. The chapter then identifies the types of competing reaction. A pre-requisite for minimisation of side reactions is to know what they are. The commonest parameters used to manipulate absolute and relative reactivities are concentration, order of reactant addition, and temperature. The chapter also considers parallel/consecutive reactions; pH-rate and selectivity profiles; and methods for predicting reactivity.
Chapter
Integrated rate laws
This chapter focuses on how the composition of a reaction mixture can be predicted by
integrating a rate law. An integrated rate law is an expression that gives the concentration
of a species as a function of the time. They are called integrated rate laws because a rate
law is a differential equation, and solving such an equation involves the mathematical
technique of integration. Integrated rate laws have two principal uses. One is to predict
the concentration of a species at any time after the start of the reaction. Another is to
help find the rate constant and order of the reaction. The chapter then looks at the
integrated rate laws for a variety of simple reaction types, including zeroth-order
reactions, first-order reactions, and second-order reactions. It also considers the concept
of half-life.
Chapter
Preparing and measuring reagents
Ian Graham
This chapter details the process of preparing and measuring reagents, which are essential and fundamental skills for all biomedical scientists. The use of balances for weighing and pipettors and other volume measurement methods for volume delivery are key techniques in the production of solutions and their dilution. For correct operation, balances must be appropriately sited and calibrated. Burettes, pipettes, and volumetric flasks provide high levels of accuracy if used correctly. However, pipettors are the volume measurement tool of choice for highly accurate and precise work. They use disposable tips for convenience, require calibration, and, being precision instruments, must be used with care. The chapter then looks at molar concentrations and alternative ways of expressing concentration.
