FE Chemical key terms

An accounting of the mass entering, leaving, accumulating in, or being generated within a system, written so that total mass in equals total mass out plus accumulation. It is the starting point for sizing equipment and checking data consistency.

An accounting of all energy crossing a system boundary plus internal generation and accumulation, typically combining enthalpy changes, sensible and latent heat, and shaft work. It underlies heat exchanger and reactor design and utility estimates.

A chosen reference quantity, such as 100 mol or 1 kg of feed, on which a calculation is set up. Selecting a convenient basis simplifies degrees-of-freedom analysis and lets results be scaled later.

The number of independent unknowns minus the number of independent equations relating them. A value of zero means the system can be solved; negative means it is over-specified and positive means more data are needed.

Recycle returns unreacted material to a reactor to raise conversion; purge removes a small slipstream to prevent inert or byproduct buildup. Together they control steady-state impurity concentration and overall yield.

Single-pass conversion is the fraction of feed reacted in one pass through the reactor; overall conversion includes recycled material. Overall conversion is always higher when a recycle loop is present.

A single variable that tracks how far each reaction has progressed, equal to moles reacted divided by the stoichiometric coefficient. It converts multi-reaction balances into a compact set of linear equations.

The limiting reactant is consumed first if the reaction goes to completion; excess is the percentage by which other reactants exceed the stoichiometric amount required by the limiting one. These set maximum yield and selectivity.

Selectivity is the moles of desired product formed per mole of undesired product or per mole of reactant consumed; yield is product formed per reactant fed. Both matter when competing reactions occur.

The ideal gas law relates pressure, volume, moles, and temperature; the compressibility factor Z corrects it for real-gas behavior at high pressure. Z near one indicates near-ideal behavior.

A mathematical relation among pressure, volume, and temperature for a substance, such as cubic or virial forms. It is used to estimate density, phase behavior, and departure from ideality in process calculations.

The condition in which vapor and liquid phases coexist with equal fugacity of each component, often expressed through K-values or relative volatility. It governs flash drums, distillation, and absorber design.

The ratio of K-values of two components, indicating how easily they can be separated by distillation. Values far from one mean an easy split; values near one require many stages or a different separation method.

Partial pressure is a component's mole fraction times total pressure in an ideal gas mixture; fugacity is a corrected pressure that accounts for nonideality. Fugacity is the proper driving force in phase equilibrium.

The heat released or absorbed when a reaction proceeds at constant pressure, computed from heats of formation or combustion. Its sign and magnitude set reactor heat duties and cooling requirements.

The temperature increase a reacting stream would experience with no heat exchange, found by balancing the heat of reaction against sensible heat. It indicates runaway risk and coolant needs.

Heat capacity is the energy needed to raise a substance's temperature per unit amount; latent heat is the energy absorbed during a phase change at constant temperature. Both are needed for sensible and phase-change duties.

Batch distillation separates a charge over time while composition shifts; the Rayleigh equation relates remaining liquid amount and composition to the instantaneous vapor composition. It estimates batch yields and end points.

A graphical stage-counting technique using an operating line and an equilibrium curve to estimate theoretical distillation stages. It shows how reflux ratio and feed condition affect stage requirements.

The ratio of liquid returned to the top of a distillation column to distillate withdrawn. Higher reflux improves purity but raises energy use; minimum reflux corresponds to infinite stages.

Operations that transfer moisture between a gas and a solid or liquid, described by humidity charts and psychrometric data. They are used to dry solids and to control gas moisture content.

Extraction transfers a solute from one liquid phase to another immiscible solvent; leaching removes soluble material from a solid. Both rely on equilibrium distribution and staged contacting.

Absorption transfers a gas component into a liquid solvent; stripping removes it from the liquid. Design uses equilibrium solubility, operating lines, and transfer units.

A dimensionless ratio of inertial to viscous forces that indicates whether flow is laminar, transitional, or turbulent. It guides friction factor and heat and mass transfer correlations.

The friction factor quantifies flow resistance in pipes and fittings; combined with velocity and density it gives pressure drop through the Darcy-Weisbach or equivalent relations. It sets pump duty.

The mechanical energy balance relates pressure, velocity, elevation, and friction losses along a flow path. It is the standard tool for sizing pumps and evaluating pipe networks.

The pump curve shows head delivered versus flow; the system curve shows head required. Their intersection is the operating point, which shifts when valves or equipment change resistance.

A dimensionless ratio of convective to conductive heat transfer at a surface, used in correlations to predict heat transfer coefficients. It typically depends on Reynolds and Prandtl numbers.

The effective average temperature driving force in a heat exchanger, computed from terminal hot and cold stream temperatures. It accounts for the reduced driving force when flow is countercurrent or co-current.

The combined resistance to heat transfer across a wall, including convection on both sides and conduction through the wall. It is used with area and log mean temperature difference to find heat duty.

An added thermal resistance representing deposits that build up on heat transfer surfaces over time. It forces extra area to be installed so duty can still be met between cleanings.

Two approaches to heat exchanger analysis: one uses log mean temperature difference and area, the other uses effectiveness and number of transfer units. The second is convenient when outlet temperatures are unknown.

A proportionality constant relating a molar flux to a concentration difference between bulk fluid and an interface. It is estimated from correlations and used in absorber, dryer, and extraction design.

A rate law expresses reaction rate as a function of concentrations; the Arrhenius equation gives the rate constant's temperature dependence through activation energy. Together they predict how reactors respond to conditions.

Design equations relating reactor volume, feed rate, conversion, and rate for batch, CSTR, plug-flow, and packed-bed reactors. They determine the volume needed to reach a target conversion.

The spread of times that material spends in a vessel, reflecting mixing and flow patterns. It helps diagnose bypassing or dead zones and assess whether a real reactor behaves ideally.

A catalyst speeds a reaction without being consumed; turnover frequency is the number of catalytic cycles per active site per time. It measures intrinsic activity and guides catalyst selection.

A system at equilibrium shifts to counteract a change in temperature, pressure, or concentration. It predicts whether higher pressure or lower temperature favors a desired equilibrium-limited reaction.

A ratio of product to reactant activities at equilibrium, dependent on temperature. It sets the maximum attainable conversion for reversible reactions and appears in reactor design and phase equilibrium calculations.