ENADE Engenharia Química cheat sheet

Professional ethics codes (e.g., CONFEA/CREA resolutions in Brazil) bind engineers to public safety, health, and welfare above client or employer interests.

Whistleblowing is justified when disclosure prevents imminent harm to life, health, or environment and internal channels have failed or are unsafe.

Conflict of interest exists when a secondary interest (financial, familial, political) could improperly influence professional judgment; disclose and recuse.

Informed consent requires disclosing risks, alternatives, and uncertainties in language the affected party can understand before action.

Plagiarism includes copying text, data, figures, or code without attribution; self-plagiarism of prior published work also violates publication ethics.

Confidentiality obligations persist after employment ends; exceptions arise from legal subpoena, imminent danger, or explicit client waiver.

Sustainable development (Brundtland, 1987) means meeting present needs without compromising future generations' ability to meet theirs.

Citizenship duties of engineers include compliance with environmental licensing, worker safety norms (NRs), and honest public communication of risk.

Falsifying or selectively reporting experimental data violates research integrity and can constitute fraud under professional codes.

Precautionary principle: lack of full scientific certainty is not grounds for postponing cost-effective measures to prevent serious or irreversible harm.

Polluter-pays principle assigns remediation and prevention costs to the party responsible for contamination.

Life Cycle Assessment (LCA) follows ISO 14040/14044 stages: goal and scope, inventory, impact assessment, interpretation.

Greenhouse gases differ in global warming potential; CO2 = 1, CH4 ≈ 28-30, N2O ≈ 265-298 over 100 years (AR5 values).

Renewable share of Brazilian electricity is high (~80%+) due to hydropower, wind, and biomass, unlike the global average (~30%).

Technology transfer and appropriate technology debates weigh capital intensity, local employment, and maintenance capability.

Risk = probability × consequence; risk communication must address perception gaps between specialists and lay publics.

Environmental impact assessment (EIA/RIMA in Brazil) precedes licensing and requires public consultation for major projects.

Circular economy replaces end-of-pipe treatment with design for reuse, remanufacture, and material recovery.

An argument has premises (evidence) and a conclusion (claim); validity concerns structure, soundness also requires true premises.

Deductive arguments guarantee conclusions if premises are true; inductive arguments make conclusions probable only.

Common fallacies: ad hominem, straw man, false dilemma, appeal to authority without expertise, post hoc ergo propter hoc, slippery slope.

Technical writing favors active or clear passive voice, defined acronyms at first use, SI units, and one idea per paragraph.

Cohesion uses referential chains (pronouns, synonyms); coherence concerns logical consistency of the whole text with its purpose.

Data interpretation must distinguish correlation from causation and report uncertainty, sample size, and measurement conditions.

Citation norms: direct quotation needs page reference; paraphrase still needs author-year attribution.

In ENEM/ENADE-style essays, the proposal must address the problem with feasible, detailed, rights-respecting actions.

General balance: accumulation = input − output + generation − consumption; applies to mass, moles, energy, and species.

Steady state with no reaction: Σ inputs = Σ outputs for total mass and each component.

Extent of reaction ξ: n_i = n_i0 + ν_i ξ; used to close reactive balances with multiple reactions.

First law for open steady system: Q − W = Σ_out ṁ h − Σ_in ṁ h (neglecting KE and PE).

Entropy balance: ΔS = ∫δQ/T + S_gen, with S_gen ≥ 0; equality for reversible processes.

Phase equilibrium: fugacity equality f_i^L = f_i^V; Raoult's law for ideal mixtures, modified Raoult with γ_i for nonideal.

Activity coefficient models: Margules, van Laar, NRTL, UNIQUAC, UNIFAC (predictive group contribution).

Carnot efficiency η = 1 − T_C/T_H (absolute temperatures); real cycles always lower.

Heat of reaction at T from Hess's law plus sensible heat: ΔH_r(T) = ΔH_r(T_ref) + ∫ΔCp dT.

Reynolds number Re = ρvD/μ; pipe flow laminar below ~2100, turbulent above ~4000, transitional between.

Darcy-Weisbach: ΔP = f (L/D)(ρv²/2); friction factor from Moody chart or Colebrook equation.

Hagen-Poiseuille for laminar pipe: ΔP = 32 μ L v / D².

Bernoulli with losses: P1/ρg + v1²/2g + z1 = P2/ρg + v2²/2g + z2 + h_L.

Nusselt number correlations: Dittus-Boelter Nu = 0.023 Re^0.8 Pr^n (n = 0.4 heating, 0.3 cooling) for turbulent pipe flow.

Mass transfer: Sh = k_c L/D_AB; analogies (Chilton-Colburn) link f/2 = j_D = j_H = St·Sc^(2/3) = St·Pr^(2/3).

Fick's law: J_A = −D_AB ∇C_A; diffusion coefficient increases with temperature and decreases with pressure for gases.

Conduction: Fourier q = −k ∇T; 1D slab resistance R = L/(kA); convection R = 1/(hA).

Pumps: NPSH_available must exceed NPSH_required to avoid cavitation; affinity laws scale Q∝N, H∝N², P∝N³.

Arrhenius: k = A exp(−E/RT); ln(k2/k1) = (E/R)(1/T1 − 1/T2).

Batch design equation: t = N_A0 ∫ dX/(−r_A V); CSTR: V = F_A0 X/(−r_A); PFR: V = F_A0 ∫ dX/(−r_A).

For first-order CSTR vs PFR at equal conversion, PFR volume is always smaller; for autocatalytic or positive-order kinetics, compare carefully.

Half-life for first-order reaction is independent of initial concentration: t_1/2 = ln2/k.

Selectivity and yield depend on concentration ratios; higher C_A favors higher-order desired reaction.

Levenspiel plot (1/−r_A vs X) area gives required volume; CSTR uses rectangle, PFR uses area under curve.

Catalysis: turnover frequency (TOF) = molecules converted per active site per time; Thiele modulus and effectiveness factor η describe intraparticle diffusion limits.

Nonideal reactors: residence time distribution E(t); tracer pulse gives E(t); mean residence time τ = V/Q for constant density.

Energy balance for adiabatic CSTR: T = T0 + (−ΔH_r) X / Σθ_i Cp_i; multiple steady states possible for exothermic reactions.

Distillation McCabe-Thiele: operating lines intersect at q-line; minimum reflux from pinch point touching equilibrium curve.

Fenske equation for minimum stages at total reflux; Underwood for minimum reflux; Gilliland correlation for actual stages.

Relative volatility α_ij = K_i/K_j; easy separation when α far from 1; azeotropes require special methods (extractive, pressure-swing).

Absorption/stripping design uses Kremser equations or transfer-unit (NTU/HTU) methods.

Liquid-liquid extraction: distribution coefficient K = y/x; selectivity β = K_A/K_B; solvent choice favors high β and easy recovery.

Drying: constant-rate period controlled by external heat/mass transfer; falling-rate period controlled by internal diffusion.

Filtration: Ruth equation V² + 2V·V_0 = K·t for constant-pressure cake filtration.

Membrane separation: flux J = ΔP/(μ R_m) for pure solvent; concentration polarization reduces flux and selectivity.

Crystallization: supersaturation drives nucleation and growth; population balance links crystal size distribution to operating conditions.

PID: u(t) = Kc[e + (1/τ_I)∫e dt + τ_D de/dt]; proportional band = 100/Kc (%).

First-order plus dead time (FOPDT) model: G(s) = K e^(−θs)/(τs+1); Ziegler-Nichols tuning uses K, τ, θ or ultimate gain K_u and period P_u.

Closed-loop stability by Routh-Hurwitz, Bode (gain margin, phase margin), or Nyquist criterion.

Feedback reduces sensitivity but can destabilize; feedforward compensates measured disturbances without feedback correction.

Control valve: installed characteristic changes with pressure drop; equal-percentage valves suit wide rangeability.

Instrumentation: 4-20 mA current loop standard; thermocouples (Seebeck), RTDs (resistance), orifice plates (ΔP flow).

Process simulation: sequential-modular vs equation-oriented approaches; convergence aided by tear streams and good initial guesses.

Mass and energy balance closure is prerequisite for simulation validation; sensitivity analysis identifies dominant parameters.

Sampling and aliasing: sample rate must exceed twice the highest signal frequency (Nyquist).

Carbon steel is cheap and strong but corrodes; stainless steel (≥10.5% Cr) forms passive Cr2O3 film resisting oxidation.

Galvanic series ranks metals by potential; coupling dissimilar metals accelerates corrosion of the anodic (more active) one.

Uniform corrosion rate via Faraday: rate (mm/yr) = 3.27 × 10^-3 · (i · EW)/ρ where i in μA/cm².

Pitting and crevice corrosion attack passive films in chloride environments; use higher Mo grades (316, duplex).

Stress corrosion cracking requires susceptible alloy + tensile stress + specific environment (e.g., chlorides + austenitic SS).

Cathodic protection: sacrificial anodes (Zn, Mg, Al) or impressed current; protects the structure as cathode.

ASME Boiler and Pressure Vessel Code and NR-13 govern design, inspection, and fitness-for-service of pressure equipment.

Design pressure, corrosion allowance, and joint efficiency enter shell thickness: t = P·R/(S·E − 0.6P) + CA.

Material selection considers temperature limits, creep, hydrogen attack (Nelson curves), and cost.

HAZOP studies deviations (no, more, less, reverse, as well as, part of, other than) of process parameters against guide words.

Layer of protection analysis (LOPA) quantifies risk reduction; independent protection layers must be independent and auditable.

Flash point, autoignition temperature, and flammability limits define fire/explosion hazards; LFL/UFL bound flammable mixtures.

Inherent safety hierarchy: minimize, substitute, moderate, simplify - preferred over add-on controls.

Waste hierarchy: prevent, reduce, reuse, recycle, recover, dispose; end-of-pipe treatment is last resort.

Effluent standards in Brazil: CONAMA Resolution 357/2005 (water bodies) and 430/2011 (discharge conditions).

Economic evaluation: payback, NPV, IRR; NPV > 0 at the hurdle rate indicates viable project.

Pinch analysis sets minimum utility targets from composite curves; heat recovery reduces energy cost.

Emergency relief: PSV sizing per API 520/521; two-phase flow and reactive systems need special treatment.

Haber-Bosch ammonia: N2 + 3H2 ⇌ 2NH3, exothermic, high P (150-300 bar) and moderate T (400-500 °C) with Fe catalyst.

Contact process for sulfuric acid: S → SO2 → SO3 (V2O5 catalyst) → H2SO4; SO3 absorption in concentrated acid.

Steam cracking of naphtha produces ethylene and propylene; severity controls product slate.

Ethanol from sugarcane: fermentation of sucrose by Saccharomyces cerevisiae, distillation, and cogeneration from bagasse.

Biodiesel by transesterification of triglycerides with methanol and basic catalyst (NaOH/KOH), yielding glycerol coproduct.

Enzyme kinetics: Michaelis-Menten v = Vmax S/(Km + S); Lineweaver-Burk linearization 1/v vs 1/S.

Monod growth: μ = μmax S/(Ks + S); yield coefficient Y_X/S relates substrate to biomass.

Anaerobic digestion stages: hydrolysis, acidogenesis, acetogenesis, methanogenesis; biogas ~50-70% CH4.

Hydrogen production routes: steam methane reforming (SMR), electrolysis, biomass gasification; green H2 requires renewable electricity.

Recycle and purge balances: purge fraction controls inert buildup; steady-state inert concentration = (feed inert + recycle inert)/(total recycle) at balance.

Bypass streams reduce conversion per pass but can protect sensitive catalysts from high temperature.

Degrees-of-freedom analysis: number of independent equations must equal number of unknowns before solving.

Reference state choice is arbitrary but must be consistent; elemental balances replace reaction stoichiometry when reactions are unknown.

Psychrometric balances for humid air: humidity ratio, enthalpy, and wet-bulb temperature close drying and cooling tower balances.

Combustion: theoretical O2 from stoichiometry; excess air = (actual O2 − theoretical)/theoretical × 100; Orsat analysis gives dry flue gas composition.

Heat exchanger energy balance: Q = ṁ_h Cp_h (T_h,in − T_h,out) = ṁ_c Cp_c (T_c,out − T_c,in) with losses neglected.

Test for mass transfer limitation: vary agitation or particle size; if rate changes, external or internal diffusion controls.

Activation energy from Arrhenius plot; apparent E lower than true E signals diffusion limitation.

Differential vs integral method of rate analysis: differential uses slopes of C vs t; integral tests candidate rate laws against conversion data.

Initial rate method isolates reaction order by varying one concentration at a time.

Recycle reactor approximates CSTR behavior at high recycle ratio; PFR at low recycle ratio.

Catalyst deactivation: fouling, poisoning, sintering, and coking; time-on-stream data distinguish reversible from irreversible loss.

Safety: runaway reactions occur when heat generation exceeds removal; Semenov analysis compares rates and derivatives.

Distillation is preferred when relative volatility > 1.05-1.1 and no azeotrope; otherwise consider extraction, adsorption, or membranes.

Absorption suits dilute gas solutes with high solubility; stripping regenerates solvent by temperature or pressure swing.

Crystallization suits high-purity solids with steep solubility-temperature curves; cooling vs evaporative crystallization depends on curve slope.

Drying selection: tray for fragile solids, rotary for granular, spray for heat-sensitive slurries, fluidized bed for uniform particles.

Membrane processes: reverse osmosis for dissolved salts, ultrafiltration for macromolecules, microfiltration for particles.

Centrifugation and filtration compete on particle size and solids loading; centrifugation better for fine, compressible cakes.

Select controlled variable with high sensitivity and short dead time; manipulate variable with large gain and fast response.

Flow loops are fast and noisy: use PI control with high gain and no derivative; level loops tolerate averaging and slow tuning.

Dead time dominates controllability; reduce it by relocating sensors or changing piping before retuning.

Integral windup: clamp integral term or use anti-windup when actuator saturates.

Cascade control requires the inner loop faster than the outer loop (typically 3-5× faster).

Ratio control maintains flow ratios (e.g., air/fuel); split-range control uses one controller for two valves.

Valve stiction shows as limit cycles; diagnose by comparing controller output to valve position.

If environment is neutral and buried, use coating plus cathodic protection; if high-temperature oxidizing, use Cr/Ni alloys.

Chloride pitting resistance equivalent number PREN = %Cr + 3.3%Mo + 16%N; higher PREN resists pitting.

Erosion-corrosion accelerates at high velocity and in bends; reduce velocity or use harder alloys.

Hydrogen embrittlement affects high-strength steels; avoid cathodic overprotection and use lower-strength alloys.

Creep becomes significant above ~0.4 T_melt; design with creep-rupture data and limit stress.

Weld decay in austenitic stainless steel from Cr carbide precipitation; use low-carbon (L) grades or stabilize with Ti/Nb.

Inspection intervals derive from corrosion rate and remaining wall thickness (API 570/510).

Identify hazardous materials, inventory, and process conditions; classify per GHS and local regulations.

Determine credible accident scenarios: loss of containment, runaway reaction, overpressure, and external events.

Estimate consequence with dispersion, fire, and explosion models; estimate frequency from historical data or fault trees.

Compare risk to tolerability criteria (e.g., ALARP); document residual risk and mitigation.

Environmental permits require emission inventories, monitoring plans, and emergency response plans.

Waste minimization often yields economic returns through reduced raw material and disposal costs.

Life cycle thinking avoids shifting burdens between air, water, and soil media.

Petroleum refining: atmospheric and vacuum distillation, catalytic cracking, reforming, hydrotreating, and alkylation.

Chlor-alkali process: electrolysis of brine yields Cl2 (anode), H2 and NaOH (cathode); membrane cells dominate new capacity.

Cement: calcination of CaCO3 and clinker formation at ~1450 °C; CO2 emissions are intrinsic to calcination.

Pulp and paper: kraft pulping with NaOH/Na2S; recovery boiler regenerates chemicals and recovers energy.

Bioreactor modes: batch, fed-batch (substrate control avoids inhibition), continuous (chemostat at steady state).

Sterilization: thermal death kinetics follow first-order; D-value is time to reduce population by 90%.

Biofuels policy: RenovaBio in Brazil uses carbon intensity scores (gCO2eq/MJ) to issue decarbonization credits.

Prandtl Pr = Cp μ/k (momentum/thermal diffusivity); Schmidt Sc = μ/(ρ D_AB) (momentum/mass).

Peclet Pe = Re·Pr or Re·Sc; large Pe means convection dominates over diffusion.

Grashof number Gr = g β ΔT L³/ν²; natural convection when Gr/Re² is large.

Biot number Bi = hL/k_solid; Bi < 0.1 permits lumped capacitance analysis.

Lumped capacitance: (T − T∞)/(T0 − T∞) = exp(−hA t/(ρ V Cp)).

Radiation: q = ε σ A (T⁴ − T_surr⁴); Stefan-Boltzmann σ = 5.67×10^-8 W/(m²·K⁴).

Boundary layer: δ/L ∝ Re^(−1/2) laminar; heat and mass boundary layers relate via Pr and Sc.

Fouling resistances add in series: 1/U_dirty = 1/U_clean + R_f.