Skills

Mass and Energy Balance

6 weeks · 0 milestones

Perform a complete mass and energy balance for a real or representative chemical process, demonstrating conservation of mass and energy across each unit operation and the overall system. The balance must include: a process description identifying all feed streams, products, by-products, and waste streams, a mass balance table with inlet and outlet flows for all components (in consistent units) demonstrating closure within 1% or documenting any unaccounted losses, an energy balance covering the major energy inputs and outputs (heat of reaction, heat exchange, pump or compressor work) with documented thermodynamic data sources, and a stream summary table presenting all stream compositions, flowrates, temperatures, and pressures. Preferred proof: a mass and energy balance for a real industrial process using professional process simulation software. Accessible alternative: DWSIM (free, open-source chemical process simulator for Windows, Mac, and Linux) — simulation input file submitted alongside the results; OR a complete hand calculation for a simplified 2-3 unit process with documented data sources (NIST Chemistry WebBook for thermodynamic data — free). Proof artifacts: the process flowsheet with stream data (design artifact) and the balance tables demonstrating mass and energy closure (analysis artifact). Verification: a process engineer reviews the energy balance — 'your heat exchanger duty — what driving temperature difference are you assuming, and is that physically achievable given your stream temperatures?' — requiring you to reason from your own streams.

Part of: Engineering · Proves for: Engineers, UG

Milestone map

3 milestones

Define System Boundary and Draw Process Flow

1–2 weeks (3–4 hrs/week)

Select a real or simulated chemical process — distillation column, heat exchanger network, reaction system, or separation train. Define system boundaries clearly: which streams cross the boundary, which unit operations are inside it. Draw a process flow diagram (PFD) with all streams labelled. Proper system definition prevents the most common mass balance error: accounting for streams that should be outside the boundary.

Proof required

Submit your system definition document: the process you selected (real or simulated), a drawn PFD with all stream labels, and a list of all streams crossing the system boundary with their known and unknown compositions/flow rates.

What gets checked

PFD is drawn (not copied from a textbook) with every stream numbered and every unit operation named
System boundary is marked on the PFD as a dashed line with all crossing streams explicitly listed
Degree-of-freedom table is completed and shows zero degrees of freedom (system is fully determined)

Common mistakes

Starting calculations without a completed PFD — you cannot correctly identify system boundaries without drawing the process first
Degree-of-freedom analysis showing more unknowns than equations — the system is under-determined; add data or narrow the system boundary before proceeding to M2

Resources

Foundationstart here

Depthgo deeper

What a verifier looks for

Confirm the PFD is hand-drawn or drawn in a tool — not copied from a textbook without modification.
Confirm all streams are labelled with numbers and all unit operations are named.
Confirm the degree-of-freedom table is completed and shows zero degrees of freedom (system is fully determined).

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Perform the Mass and Energy Balances

3–4 weeks (4–5 hrs/week)

Calculate complete mass and energy balances for the system defined in M1. Mass balance: apply conservation of mass for each component across each unit operation; show all algebraic steps. Energy balance: calculate enthalpy of each stream (using heat capacity data or steam tables), heat duties for each unit operation, and total utility requirements. Showing every step is what distinguishes a competent calculation from a black-box result.

Proof required

Submit your calculation workbook (spreadsheet or written calculation set): complete mass balance tables (stream compositions and flow rates), energy balance tables (stream enthalpies, unit heat duties, utility requirements), and a summary table of results.

What gets checked

Mass balances show component-level conservation — not just total mass flow
Enthalpy data sources are cited (NIST WebBook, steam tables, or equivalent) — not unattributed values
All calculation steps are shown — not just final results in a summary table

Common mistakes

Omitting component mass balances and only reporting total mass flow — component balances are required for reactive systems or mixtures
Using inconsistent units throughout the calculation (kg/h mixed with mol/s) — choose one unit system and convert everything before calculating

Resources

Foundationstart here

Depthgo deeper

What a verifier looks for

Confirm mass balances close — in = out for each component within a stated tolerance (typically ±1% for textbook problems).
Confirm enthalpy data sources are cited — NIST WebBook, steam tables, or equivalent; not unattributed values.
Confirm all calculation steps are shown — not just final results.

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Verify Results and Write the Balance Report

2–3 weeks (2–3 hrs/week)

Cross-check mass and energy balance results using an independent verification method — degree-of-freedom recount, spot-check of a single unit, or comparison against simulation output. Write a complete balance report documenting the process, the PFD, all balance tables, data sources, assumptions, and a discussion of key sensitivities. The report is what makes the calculation an engineering artefact, not just a spreadsheet.

Proof required

Submit your completed balance report (≥1,500 words including all tables): PFD, mass balance table, energy balance table, data source list, assumption log, verification method used and results, and discussion of sensitivities (which input has the largest effect on utility requirements).

What gets checked

Independent verification method is named and results are reported (simulation comparison or independent re-derivation — not rechecking the same work)
Assumption log lists every simplifying assumption with a justification for why it is acceptable
Sensitivity analysis identifies the dominant uncertain input and states quantitatively how much utility requirements change

Common mistakes

Reporting results without stating what assumptions were made — assumptions drive balances, and a reviewer cannot evaluate results without knowing them
Skipping independent verification — transcription errors are common in large balance tables; verification is not optional

Powstik Guide

A verified mass and energy balance report.

Steps

Recount degrees of freedom.
Cross-check one unit another way.
Explain any mismatch over 1%.
Write up with PFD and tables.

Template

Check method:
| Stream | Mass in | Mass out | Error % |
|--------|---------|----------|---------|
| Unit | Energy in | Energy out | Error % |
|------|-----------|------------|---------|
Mismatches explained:

What gets sent back

No independent check.
Unexplained large errors.
Under 1,500 words.

Resources

Foundationstart here

Depthgo deeper

What a verifier looks for

Engineering Design Triad check: M1–M3 together produce a design artifact (PFD with system boundary), an analysis artifact (mass and energy balance tables with all calculation steps), and a documentation artifact (complete balance report with assumptions and verification) — confirm all three types are present.
Confirm independent verification was performed — simulation comparison or independent re-derivation, not just rechecking the same calculation.
Confirm assumptions are listed and justified — 'ideal gas assumed' without justification is insufficient.
Confirm sensitivity analysis identifies the input with the largest effect on utility requirements.
The Proof Accessibility Rule applies — DWSIM (free), ChemSep (free), NIST WebBook (free), IChemE free resources, and draw.io (free) are all accessible without plant access.

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Part of

Chemical & Process Engineering →

Related outcomes

Milestone map

3 milestones

Define System Boundary and Draw Process Flow

1–2 weeks (3–4 hrs/week)

Proof required

What gets checked

PFD is drawn (not copied from a textbook) with every stream numbered and every unit operation named
System boundary is marked on the PFD as a dashed line with all crossing streams explicitly listed
Degree-of-freedom table is completed and shows zero degrees of freedom (system is fully determined)

Common mistakes

Starting calculations without a completed PFD — you cannot correctly identify system boundaries without drawing the process first
Degree-of-freedom analysis showing more unknowns than equations — the system is under-determined; add data or narrow the system boundary before proceeding to M2

Resources

Foundationstart here

Depthgo deeper

What a verifier looks for

Confirm the PFD is hand-drawn or drawn in a tool — not copied from a textbook without modification.
Confirm all streams are labelled with numbers and all unit operations are named.
Confirm the degree-of-freedom table is completed and shows zero degrees of freedom (system is fully determined).

You'll sign in first, then come straight back here.

Perform the Mass and Energy Balances

3–4 weeks (4–5 hrs/week)

Proof required

What gets checked

Mass balances show component-level conservation — not just total mass flow
Enthalpy data sources are cited (NIST WebBook, steam tables, or equivalent) — not unattributed values
All calculation steps are shown — not just final results in a summary table

Common mistakes

Omitting component mass balances and only reporting total mass flow — component balances are required for reactive systems or mixtures
Using inconsistent units throughout the calculation (kg/h mixed with mol/s) — choose one unit system and convert everything before calculating

Resources

Foundationstart here

Depthgo deeper

What a verifier looks for

Confirm mass balances close — in = out for each component within a stated tolerance (typically ±1% for textbook problems).
Confirm enthalpy data sources are cited — NIST WebBook, steam tables, or equivalent; not unattributed values.
Confirm all calculation steps are shown — not just final results.

You'll sign in first, then come straight back here.

Verify Results and Write the Balance Report

2–3 weeks (2–3 hrs/week)

Proof required

What gets checked

Independent verification method is named and results are reported (simulation comparison or independent re-derivation — not rechecking the same work)
Assumption log lists every simplifying assumption with a justification for why it is acceptable
Sensitivity analysis identifies the dominant uncertain input and states quantitatively how much utility requirements change

Common mistakes

Reporting results without stating what assumptions were made — assumptions drive balances, and a reviewer cannot evaluate results without knowing them
Skipping independent verification — transcription errors are common in large balance tables; verification is not optional

Powstik Guide

A verified mass and energy balance report.

Steps

Recount degrees of freedom.
Cross-check one unit another way.
Explain any mismatch over 1%.
Write up with PFD and tables.

Template

Check method:
| Stream | Mass in | Mass out | Error % |
|--------|---------|----------|---------|
| Unit | Energy in | Energy out | Error % |
|------|-----------|------------|---------|
Mismatches explained:

What gets sent back

No independent check.
Unexplained large errors.
Under 1,500 words.

Resources

Foundationstart here

Depthgo deeper

What a verifier looks for

Engineering Design Triad check: M1–M3 together produce a design artifact (PFD with system boundary), an analysis artifact (mass and energy balance tables with all calculation steps), and a documentation artifact (complete balance report with assumptions and verification) — confirm all three types are present.
Confirm independent verification was performed — simulation comparison or independent re-derivation, not just rechecking the same calculation.
Confirm assumptions are listed and justified — 'ideal gas assumed' without justification is insufficient.
Confirm sensitivity analysis identifies the input with the largest effect on utility requirements.
The Proof Accessibility Rule applies — DWSIM (free), ChemSep (free), NIST WebBook (free), IChemE free resources, and draw.io (free) are all accessible without plant access.

You'll sign in first, then come straight back here.