FE Chemical Glossary
Key terms and definitions for the Chemical Engineering exam.
Mole Fraction
The ratio of the number of moles of a component to the total number of moles in a mixture. A dimensionless quantity used in phase equilibrium and mixture property calculations.
Gibbs Free Energy
A thermodynamic potential that measures the maximum reversible work obtainable from a system at constant temperature and pressure. Negative change indicates a spontaneous process.
Activation Energy
The minimum energy required for reactant molecules to undergo a chemical reaction. Appears in the Arrhenius equation relating reaction rate constant to temperature.
Raoult Law
States that the partial pressure of a component in an ideal liquid mixture equals the product of its mole fraction in the liquid and its pure-component vapor pressure.
Henry Law
States that the amount of dissolved gas in a liquid is proportional to the partial pressure of that gas above the liquid. Applies to dilute solutions where the solute obeys ideal behavior.
Mass Balance
An accounting of mass entering, leaving, accumulating in, and being generated or consumed within a system. The fundamental equation in chemical process analysis: input minus output plus generation equals accumulation.
Energy Balance
An accounting of all forms of energy (heat, work, kinetic, potential, internal) entering and leaving a system. Based on the first law of thermodynamics applied to open or closed systems.
CSTR
Continuous Stirred-Tank Reactor, an ideal reactor model where the contents are perfectly mixed so that the outlet composition equals the composition everywhere inside the reactor.
PFR
Plug Flow Reactor, an ideal reactor model where the fluid flows as a plug with no axial mixing. Concentration changes along the length of the reactor following the design equation.
Fugacity
An effective pressure that replaces the true pressure in thermodynamic equations for real gases. Accounts for non-ideal behavior and equals pressure for an ideal gas.
Compressibility Factor
The ratio of the actual volume of a gas to the volume predicted by the ideal gas law, symbolized as Z. A value of 1 indicates ideal gas behavior.
Heat Exchanger
A device that transfers heat between two fluid streams without mixing them. Common types include shell-and-tube, double-pipe, and plate exchangers. Analyzed using LMTD or effectiveness-NTU methods.
Distillation
A separation process that exploits differences in volatility between components of a liquid mixture. Uses a column with trays or packing to achieve repeated vaporization and condensation.
Stoichiometry
The quantitative relationship between reactants and products in a chemical reaction based on the balanced equation. Used to determine limiting reagent, excess, and conversion.
Le Chatelier Principle
States that if a system at equilibrium is disturbed, it shifts in the direction that partially counteracts the disturbance. Applies to changes in concentration, pressure, and temperature.
Vapor Pressure
The pressure exerted by a vapor in equilibrium with its liquid at a given temperature. Increases with temperature and is described by the Antoine or Clausius-Clapeyron equation.