# Introduction to Chemical Engineering Processes/Notation

## Base Notation (in alphabetical order)

${\displaystyle [i]_{n}}$ : Molarity of species i in stream n
a, b, c, d: Stoichiometric coefficients.
A: Area
C: Molar concentration (mol/L)
K: Equilibrium coefficient
m: Mass
MW: Molecular Weight (Molar Mass)
n: Moles
n: Number of data points (in statistics section)
N: Number of components
P: Pressure
r: Regression coefficient
R: Universal gas constant
T: Temperature
v: Velocity
V: Volume
x: Mole fraction in the liquid phase OR Mass fraction [1]
X: (molar) extent of reaction
y: Mole fraction in the gas phase
z: Overall composition
Z: Compressibility

1. Unless specified explicitly, assume that a given percent composition is in terms of the overall flowrate. So if you're given a flowrate in terms of kg/s and a compositoin of 30%, assume that the 30% is a mass fraction. If a given equation requires one or the other, it will explicitly be stated near the equation which is necessary.

## Greek

${\displaystyle \rho }$: Density
${\displaystyle \Sigma }$: Sum


## Subscripts

If a particular component (rather than an arbitrary one) is considered, a specific letter is assigned to it:

• [A] is the molarity of A
• ${\displaystyle x_{A}}$ is the mass fraction of A

Similarly, referring to a specific stream (rather than any old stream you want), each is given a different number.

• ${\displaystyle {\dot {n}}_{1}}$ is the molar flowrate in stream 1.
• ${\displaystyle {\dot {n}}_{A1}}$ is the molar flow rate of component A in stream 1.

Special subscripts:

If A is some value denoting a property of an arbitrary component stream, the letter i signifies the arbitrary component and the letter n signifies an arbitrary stream, i.e.

• ${\displaystyle A_{n}}$ is a property of stream n. Note ${\displaystyle {\dot {n}}_{n}}$ is the molar flow rate of stream n.
• ${\displaystyle A_{i}}$ is a property of component i.

The subscript "gen" signifies generation of something inside the system.

The subscripts "in" and "out" signify flows into and out of the system.

## Embellishments

If A is some value denoting a property then:

${\displaystyle {\bar {A}}_{n}}$ denotes the average property in stream n

${\displaystyle {\dot {A}}_{n}}$ denotes a total flow rate in steam n

${\displaystyle {\dot {A}}_{in}}$ denotes the flow rate of component i in stream n.

${\displaystyle {\hat {A}}}$ indicates a data point in a set.

${\displaystyle A_{i}^{*}}$ is a property of pure component i in a mixture.

## Units Section/Dimensional Analysis

In the units section, the generic variables L, t, m, s, and A are used to demonstrate dimensional analysis. In order to avoid confusing dimensions with units (for example the unit m, meters, is a unit of length, not mass), if this notation is to be used, use the unit equivalence character ${\displaystyle {\dot {=}}}$ rather than a standard equal sign.