1. Electrochemical Science and Technology: Fundamentals and Applications, Keith B. Oldham, Jan C. Myland and Alan M. Bond. © 2011 John Wiley & Sons, Ltd. Published 2011 by John Wiley & Sons, Ltd. Figure 2.1 Up to very high pressures, the activity of a gas is proportional to its partial pressure.

2. Electrochemical Science and Technology: Fundamentals and Applications, Keith B. Oldham, Jan C. Myland and Alan M. Bond. © 2011 John Wiley & Sons, Ltd. Published 2011 by John Wiley & Sons, Ltd. Figure 2.2 The activity of a solute behaving ideally would equal c i /c° at all concentrations. Ionic solutes depart from ideality much sooner than do nonionic solutes.

3. Electrochemical Science and Technology: Fundamentals and Applications, Keith B. Oldham, Jan C. Myland and Alan M. Bond. © 2011 John Wiley & Sons, Ltd. Published 2011 by John Wiley & Sons, Ltd. Figure 2.3 The Gibbs energy of a substance varies logarithmically with its activity, equaling its standard value G° at unit activity.

4. Electrochemical Science and Technology: Fundamentals and Applications, Keith B. Oldham, Jan C. Myland and Alan M. Bond. © 2011 John Wiley & Sons, Ltd. Published 2011 by John Wiley & Sons, Ltd. Figure 2.4 The transfer of an uncharged substance i, between Reservoirs L and R, can be made directly but, for a charged species, it is convenient to imagine travel through an intermediate Reservoir I.

5. Electrochemical Science and Technology: Fundamentals and Applications, Keith B. Oldham, Jan C. Myland and Alan M. Bond. © 2011 John Wiley & Sons, Ltd. Published 2011 by John Wiley & Sons, Ltd. Figure 2.5 In water, the activities of the hydronium and hydroxide ions are interrelated by The pH is defined as.

6. Electrochemical Science and Technology: Fundamentals and Applications, Keith B. Oldham, Jan C. Myland and Alan M. Bond. © 2011 John Wiley & Sons, Ltd. Published 2011 by John Wiley & Sons, Ltd. Figure 2.6 The ionic atmosphere is pictured as a cloud of electricity, of sign opposite to that of the central ion.

7. Electrochemical Science and Technology: Fundamentals and Applications, Keith B. Oldham, Jan C. Myland and Alan M. Bond. © 2011 John Wiley & Sons, Ltd. Published 2011 by John Wiley & Sons, Ltd. Figure 2.7 The Debye-Hückel model in its limiting version predicts that the mean ionic activity coefficients of salts depend on (z + z – ) 2 μ; according to the red line. The points show experimental data for potassium fluoride and calcium chloride solutions. The predictions of the extended law for z + z – = –1 cases are shown in green and those for z + z – = –2 are in violet.

8. Electrochemical Science and Technology: Fundamentals and Applications, Keith B. Oldham, Jan C. Myland and Alan M. Bond. © 2011 John Wiley & Sons, Ltd. Published 2011 by John Wiley & Sons, Ltd. Figure 2.8 In the extended version of the Debye-Hückel model the ion cloud extends inwards only as far as a sphere of radius R c.

9. Electrochemical Science and Technology: Fundamentals and Applications, Keith B. Oldham, Jan C. Myland and Alan M. Bond. © 2011 John Wiley & Sons, Ltd. Published 2011 by John Wiley & Sons, Ltd. Figure 2.9 Some of the processes that may be involved in a heterogeneous reaction.