There are seven base units within the International System of Units (SI system), as shown in Table 1.1 for quick reference. Except for luminous intensity, all of the quantities are used extensively in this text. Among the base units is electric current, I, which is critical for the examination of electrochemical systems. Electric current is measured in amperes [A].
Table 1.1 The Seven SI Base Units; All Except Candela Are Used Frequently in This Book
| Quantity | Name of unit | Symbol for unit | Nomenclature used in text |
| Length | meter | [m] | L |
| Mass | kilogram | [kg] | m |
| Mole | mole | [mol] | ni |
| Time | second | [s] | t |
| Temperature | kelvin | [K] | T |
| Current | ampere | [A] | I |
| Luminous intensity | candela | [cd] | – |
Table 1.2 presents derived units that are used widely in this text and are associated with electrochemical engineering. For each quantity, the name and the SI symbol for the quantity is presented. Our general practice will be to place units in brackets, for example, [Pa-s]. When working problems, dimensional consistency is critical; it will also help you to avoid calculation errors. Therefore, for convenience, the table provides the dimensions of these derived quantities written in terms of both the base units and in an alternative form convenient for calculations. For instance, the units for capacitance [m−2·kg−1·s4·A2] can be written more compactly in terms of other derived units [C·V−1], which will usually be more intuitive and easier to remember when checking for dimensional consistency. Finally, the last column provides the variable symbol used in this text to represent the physical quantity. Where possible, we have used the most common nomenclature to represent these quantities. A detailed list of the nomenclature is provided at the beginning of the book. It is important to note that sometimes the nomenclature for a variable may be the same as the unit. To minimize confusion, remember that variables and fundamental physical constants are in italics, whereas the units will not be italicized. Thus, V represents the potential of an electrochemical cell, whose units are volts [V]. Similarly, A is area [m2], whereas [A] is the unit for current in amperes. Most often we will be dealing with scalar quantities. However, occasionally we will encounter vector quantities, ones that have both magnitude and direction. These quantities will be written in bold face. For example, velocity, a vector quantity, is written with the symbol v.
Table 1.2 SI Derived Units That Are Important for This Text
| Quantity | Name of unit | Symbol for unit | Expressed in SI base units | Alternative expression | Nomenclature used in text |
| Electric charge | coulomb | [C] | A·s | [F·V] | Q |
| Potential | volt | [V] | m2·kg·s−3·A−1 | [A·Ω], [J·C−1] | V, ϕ |
| Capacitance | farad | [F] | m−2·kg−1·s4·A2 | [C·V−1] | C |
| Resistance | ohm | [Ω] | m2·kg·s−3·A−2 | [V·A−1] | RΩ |
| Electrical conductance | siemens | [S] | m−2·kg−1·s3·A2 | [A·V−1], [Ω−1] | S |
| Force | newton | [N] | m·kg·s−2 | – | Fx |
| Pressure | pascal | [Pa] | kg·m−1·s−2 | [N·m−2] | p |
| Energy | joule | [J] | m2·kg·s−2 | [N·m] | E |
| Power | watt | [W] | m2·kg·s−3 | [J·s−1] | P |
| Frequency | hertz | [Hz] | s−1 | – | f |
The coulomb [C] is an SI-derived unit of electrical charge—simply the amount of charge that passes with a current of 1 ampere for 1 second. The elementary charge, denoted with q, is a fundamental physical constant. The value of q is 1.602177 × 10−19 C and equal to the charge of a single proton. Additional essential fundamental constants are provided in Appendix B.
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