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STUDY GUIDE · GKU 1

Material and energy balances study guide (Chemical Engineering)

Every calculation in chemical engineering starts with the same sentence: what goes in, minus what comes out, plus what is made, minus what is used up, equals what accumulates. This guide teaches that sentence and its uses. It begins with the variables a balance is written in (flows, compositions, pressures, temperatures) and with degrees of freedom, which tell you before you start whether a problem can be solved. It then writes steady-state material balances on single units and on flowsheets of several units, handles recycle, bypass and purge streams, and adds chemical reaction through the extent of reaction, atom balances and combustion with excess air. The energy balance follows, with sensible and latent heat and the heat of reaction from heats of formation, and then humid air and the psychrometric chart. The last section drops the steady-state assumption and solves the balances as differential equations for tanks that fill, mix and heat up.

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Structured by the official ETEC subject standard for this topic: every listed topic and learning outcome, with formulas, figures and worked examples. The full sections are available to members in the app.

SKU 1.1 · Mass and energy balance

  1. Process variables and degrees of freedom

    The quantities a balance is written in (flows, fractions, pressures, temperatures), how to convert between them, and how a degree-of-freedom count tells you whether a problem can be solved and in what order.

  2. Steady-state material balances

    In-equals-out balances on single units and on flowsheets of several units: choosing envelopes, using tie components, and solving a sequence of units without simultaneous equations.

  3. Recycle, bypass and purge

    Why streams are recycled, bypassed and purged, how overall and single-pass conversion differ, and how to solve a flowsheet with a recycle loop directly or by iteration.

  4. Reactive systems and combustion

    Material balances with chemical reaction: extent of reaction, limiting and excess reactants, conversion, yield and selectivity, atom balances, and combustion with excess air on wet and dry bases.

  5. Steady-state energy balances

    The steady-flow energy balance for process units, sensible and latent heat, heats of reaction from heats of formation, and the energy balance on a reactor up to the adiabatic flame temperature.

  6. Humid air and the psychrometric chart

    Humidity, relative humidity, dew point and wet-bulb temperature, how the psychrometric chart organises them, and how to write material and energy balances on dryers, humidifiers and air coolers on a dry-air basis.

  7. Unsteady-state material and energy balances

    Balances in which something accumulates: tanks filling and emptying, the composition of a mixing tank after a feed change, the temperature of a heated tank, and the start-up of a reactor, solved as first-order differential equations.

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