Key Vocabulary – Chemical Engineering Calculations & Principles

Vocabulary flashcards covering fundamental terms and concepts appearing in the lecture’s quantitative problems on material balances, separation processes, reaction stoichiometry, and combustion calculations.

Specific Gravity (SG)

The ratio of the density of a substance to the density of a reference substance (usually water at 4 °C for liquids). Dimensionless.

Mass Fraction

The mass of a component divided by the total mass of the mixture; expressed as a decimal (e.g., 0.20).

Weight Percent (wt %)

The mass fraction of a component multiplied by 100; mass of component per 100 units of total mass.

Mole Fraction (x or y)

The ratio of moles of a component to the total moles in a mixture.

Mole Percent (mol %)

Mole fraction multiplied by 100; moles of component per 100 moles of mixture.

Solution Concentration

A quantitative measure of the amount of solute present per unit amount of solution or solvent (e.g., wt %, molarity, molality).

Feed Ratio

The proportion of two or more feed streams combined before entering a process unit (e.g., liters of 20 % acid per liter of 60 % acid).

Recycle Ratio

The mass or moles of recycle stream divided by the mass or moles of fresh feed entering a process.

Single-Pass Conversion

The fraction of a reactant consumed in one pass through a reactor, ignoring any recycle.

Overall Conversion

The fraction of a reactant consumed relative to the fresh feed, including the effects of recycle and multiple passes.

Limiting Reactant

The reactant present in the smallest stoichiometric amount; it determines the maximum possible extent of reaction.

Excess Reactant

A reactant present in greater quantity than required by stoichiometry, remaining after the limiting reactant is consumed.

Percent Excess

[(Actual amount – Stoichiometric amount) / Stoichiometric amount] × 100; quantifies how much excess reactant is supplied.

Percent Conversion

(Moles (or mass) reacted of a species / Moles (or mass) fed of that species) × 100.

Evaporator

Equipment that removes solvent (often water) from a solution by boiling, thereby concentrating the solute.

Crystallization

A separation technique in which a solute forms solid crystals from a solution when conditions (e.g., temperature) change.

Solubility

The maximum amount of solute that can dissolve in a given amount of solvent at specified conditions, often expressed as g solute/100 g solvent.

Saturated Solution

A solution that contains the maximum amount of dissolved solute at equilibrium under given conditions.

Mother Liquor

The residual solution remaining after crystals or precipitate have been removed from a crystallizer.

Reflux

The portion of condensed overhead vapor returned to the top of a distillation column to improve separation.

Boil-up

Vapor generated in a reboiler and sent upward into a distillation column.

Partial Reboiler

A reboiler that vaporizes only a fraction of the bottom liquid, sending vapor back to the column and withdrawing the remaining liquid as bottoms.

Azeotrope

A mixture of two or more substances that boils at a constant temperature and composition, behaving as a single component during distillation.

Batch Distillation

Distillation carried out on a fixed charge of liquid, with products withdrawn over time until the run is stopped.

Dry Basis

Composition expressed after all moisture has been theoretically removed from a sample.

Wet Basis

Composition expressed relative to the total mass, including moisture present.

Moisture Content

The amount of water present in a material, often expressed as wt % wet basis or dry basis.

Dry Air

Air that contains no water vapor; often assumed in combustion and gas calculations for simplification.

Orsat Analysis

A volumetric (dry) analysis of flue gas measuring CO₂, O₂, CO (and sometimes other gases) using an Orsat apparatus.

Stack Gas

Exhaust gases discharged from a combustion system’s chimney or stack.

Excess Air

Air supplied beyond the theoretical requirement for complete combustion, expressed as a percentage of the theoretical air.

CO/CO₂ Ratio

The proportion of carbon monoxide to carbon dioxide in combustion products; indicates combustion completeness.

Calorific Value (Heating Value)

The energy released as heat when a fuel is burned completely; expressed in MJ /kg or Btu /lb.

Fixed Carbon (FC)

The solid combustible residue left after volatile matter is released from coal; determines char yield.

Volatile Combustible Matter (VCM)

Materials in coal that vaporize and burn when heated; expressed as a percentage of coal mass.

Combined Water

Water chemically bound in a material (e.g., hydrated salts); distinguished from free moisture.

Octane Number

A measure of gasoline’s resistance to knocking, defined relative to isooctane (100) and n-heptane (0).

Cetane Number

A measure of diesel fuel’s ignition quality; based on a scale where cetane (n-hexadecane) is 100 and methyl naphthalene is 0.

Dehumidification

The removal of water vapor from air, typically by cooling below the dew point or by adsorption.

Scrubber (Gas Absorber)

Equipment that removes soluble or reactive components from a gas by contact with a liquid solvent.

Absorption

Transfer of one or more species from a gas phase into a liquid solvent with which they are more soluble.

Extraction (Leaching)

Separation process where a solute is removed from a solid (or liquid) by dissolving it in a suitable solvent.

Material Balance

An accounting of mass entering, leaving, accumulating, and generated within a process system.

Degree of Completion (Reaction Extent)

The fraction of a chemical reaction that has proceeded relative to its stoichiometric limit.

Stoichiometric Air

The exact amount of air supplying the oxygen required for complete combustion of a fuel with no excess.

Recycle Stream

A process stream that returns unconverted reactants or solvent back to an earlier stage of the process.

Mother Liquor Recycle

Returning the liquid remaining after crystallization back to the evaporator or upstream unit to recover dissolved solute.

Stack Gas Dew Point

The temperature at which water vapor in flue gas begins to condense at stack pressure and composition.