ChE Board flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Extent of reaction

A single variable that tracks how far a reaction has proceeded; species moles equal initial moles plus stoichiometric coefficient times extent, and one extent exists per independent reaction.

Limiting reactant

The reactant that is completely consumed first, found as the smallest ratio of initial moles to stoichiometric requirement; it sets the maximum possible conversion and product yield.

Reynolds number

The dimensionless ratio of inertial to viscous forces, Re = ρvD/μ; values below about 2100 indicate laminar pipe flow, above 4000 turbulent flow.

Bernoulli mechanical energy balance

Relates pressure, velocity, and elevation head between two points in a flowing fluid, with pump work added and friction loss subtracted; valid for steady incompressible flow along a streamline.

Log mean temperature difference

The driving force for heat transfer in a exchanger, computed as the difference of terminal temperature differences divided by the natural log of their ratio.

Dittus-Boelter equation

A turbulent internal-flow correlation, Nu = 0.023 Re^0.8 Pr^n, with exponent 0.4 when the fluid is heated and 0.3 when it is cooled.

Fourier law of conduction

Heat flux is proportional to the negative temperature gradient, q = -kA dT/dx; thermal resistances of wall layers in series add directly for composite plane walls.

Dalton law partial pressure

Each gas in an ideal mixture exerts pressure proportional to its mole fraction, p_i = y_i P; total pressure is the sum of the component partial pressures.

Raoult law vapor-liquid equilibrium

For ideal mixtures, y_i P = x_i P_i^sat; the ratio of vapor pressures gives relative volatility, which determines ease of distillative separation.

Fenske equation

Estimates minimum theoretical stages for distillation at total reflux using the geometric mean relative volatility and the distillate and bottoms compositions of the light key.

Kremser absorption factor

Absorption factor A = L/(mV) compares liquid and vapor flow to equilibrium; when A is near one, many stages are needed for a given solute removal.

Arrhenius equation

Rate constant varies as k = A exp(-E_a/RT); plotting natural log of k against inverse temperature yields a straight line with slope minus activation energy over R.

CSTR design equation

For steady state, reactor volume equals molar feed rate of limiting reactant times conversion divided by reaction rate evaluated at the exit composition.

PFR design equation

Reactor volume equals feed rate times the integral of reciprocal reaction rate over conversion from zero to the specified outlet conversion.

First-order batch reactor

For constant volume, the negative natural log of one minus conversion equals rate constant times time; half-life equals 0.693 divided by the rate constant.

Gibbs free energy criterion

At constant temperature and pressure, a process is spontaneous when the change in Gibbs energy is negative and at equilibrium when it is zero.

Clausius-Clapeyron equation

Relates vapor pressure to temperature through the heat of vaporization; plotting log pressure versus inverse temperature gives a slope proportional to enthalpy of vaporization.

Throttling process

Flow through a valve or porous plug with negligible heat transfer and work is isenthalpic; ideal gases do not change temperature, while real gases may cool or heat.

Psychrometric humidity ratio

Mass of water vapor per mass of dry air, computed as 0.622 times partial pressure of water divided by total pressure minus that partial pressure.

Selectivity in multiple reactions

The ratio of desired product formed to undesired product formed, or to reactant consumed; it is improved by favoring kinetics of the desired reaction path.

Flash point

The lowest temperature at which a liquid releases enough vapor to form an ignitable mixture near its surface; closed-cup tests generally report lower values than open-cup tests.

Flammable limits

The lower and upper vapor concentrations in air that can support combustion; below the lower limit the mixture is too lean, above the upper limit too rich.

HAZOP study

A team-based qualitative hazard review that applies guide words to process parameters at defined nodes to identify deviations and their potential causes and consequences.

Layer of protection analysis

A semi-quantitative risk method that assigns credit to independent protection layers and compares mitigated event frequency against a tolerable risk target.

Six-tenths rule

Equipment cost scales with capacity raised to about 0.6, so cost ratio equals size ratio to that exponent; used for preliminary capital estimates.

Lang factor

A multiplier applied to delivered equipment cost to estimate total fixed capital, accounting for installation, piping, instrumentation, and indirect costs.

Payback period

The time required for cumulative cash flows to recover fixed capital investment; computed as capital divided by annual net cash flow when flows are uniform.

Net present value

The sum of discounted future cash flows minus initial investment; a positive value at the hurdle rate indicates an economically acceptable project.

Fick first law

Diffusive molar flux is proportional to the negative concentration gradient, J = -D dC/dx; the proportionality constant is the binary diffusion coefficient.

Overall mass transfer coefficient

Combines individual film coefficients and equilibrium distribution into one resistance; the slower film usually controls the transfer rate.

Constant-pressure cake filtration

Filtrate volume versus time follows a quadratic relation; plotting time over volume against volume gives a straight line whose slope reflects cake resistance.

Langmuir isotherm

Adsorption capacity approaches a saturation limit as concentration rises, described by q = q_max K C divided by one plus K C.