Material and Energy Balances

A. Steady-state mass balance

Material Balances and Degrees of Freedom

The steady-state total and component mass balance, degrees-of-freedom analysis, tie components, and a disciplined recipe for solving multi-unit flowsheets.

Material balances are the grammar of chemical engineering: before you size a reactor, design a column, or rate a scrubber, you account for every kilogram and every mole that enters and leaves a control volume. On the FE the Material and Energy Balances topic carries one of the largest blocks of questions, and most of them are won or lost not on chemistry but on bookkeeping — picking the right control volume, counting unknowns against equations, and refusing to mix a mass basis with a mole basis. The balance idea itself is one line from the FE Reference Handbook (the Chemical Engineering and Thermodynamics chapters frame it as conservation applied to a defined system): what accumulates inside a boundary equals what comes in, minus what goes out, plus what reaction generates. Everything in this concept is that one statement, applied with discipline.

The general balance and its steady-state form

Draw a boundary around whatever you are analyzing — one unit, a cluster of units, or the whole plant — and write the balance for total mass or for any single species. For a non-reactive species the generation term vanishes; at steady state the accumulation term vanishes too, leaving the workhorse statement that input equals output. Total mass is always conserved (atoms cannot be created), so the total balance holds even when reactions occur; only per-species (component) balances pick up a generation term — whether written in moles or in mass — while the total mass balance never does.

A. Steady-state mass balance

Material Balances and Degrees of Freedom

The general balance and its steady-state form

Total versus component balances

Degrees-of-freedom analysis

Tie components

Solving multi-unit flowsheets

Exam strategy

Key equations

Worked examples

Common pitfalls

References

B. Unsteady-state mass balance

Unsteady-State Mass Balances

C. Steady-state energy balance

Steady-State Energy Balances

D. Unsteady-state energy balance

Unsteady-State Energy Balances

E. Recycle/bypass processes

Recycle, Bypass and Purge

F. Reactive systems

Reactive Systems: Extent, Conversion and Combustion