AMIE Section B Chemical flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

First law closed system

ΔU = Q − W. Change in internal energy equals heat added to system minus work done by system. Sign convention: Q positive into system, W positive by system.

Carnot efficiency

Maximum theoretical efficiency of a heat engine operating between T_H and T_C: η = 1 − T_C/T_H. Temperatures must be in absolute scale (Kelvin).

Fugacity coefficient

φ_i = f_i/(y_i P) for a component in a gas mixture. It measures deviation from ideal gas behavior; φ_i = 1 for ideal gas. Used in phase equilibrium calculations.

Reynolds number

Re = ρvD/μ (or Dvρ/μ). Ratio of inertial to viscous forces. Laminar pipe flow Re < 2100; turbulent Re > 4000; transitional between.

Fick's first law

J_A = −D_AB dC_A/dz. Molar flux of A relative to molar average velocity is proportional to concentration gradient. D_AB is diffusivity of A in B.

Log mean temperature difference

ΔT_lm = (ΔT1 − ΔT2)/ln(ΔT1/ΔT2). Used in heat exchanger design: Q = U A ΔT_lm for countercurrent or co-current flow. For multipass, multiply by correction factor F.

CSTR design equation

V = F_A0 X/(-r_A). For continuous stirred-tank reactor at steady state, outlet composition equals reactor composition. Assumes perfect mixing.

Arrhenius equation

k = A exp(−E/RT). Rate constant increases exponentially with temperature. E is activation energy, A is pre-exponential factor. Plot ln k vs 1/T gives slope −E/R.

PFR design equation

V = F_A0 ∫_0^X dX/(-r_A). For plug flow reactor, composition varies along length; no axial mixing. For constant density: τ = C_A0 ∫ dX/(-r_A).

Hoop stress in cylinder

σ_θ = Pr/t for thin-walled cylindrical pressure vessel. Circumferential stress is twice longitudinal stress (σ_L = Pr/(2t)). ASME code uses t = Pr/(SE − 0.6P) + CA.

NPSH available

NPSH_A = (P_atm − P_v)/(ρg) + z − h_f. Net positive suction head available at pump inlet. Must exceed NPSH_required to avoid cavitation.

Six-tenths rule

C2 = C1 (Q2/Q1)^0.6. Cost-capacity relationship for equipment. Used for preliminary cost estimation when capacity changes. Exponent typically 0.6 but varies by equipment type.

HAZOP guide words

NO, MORE, LESS, REVERSE, AS WELL AS, PART OF, OTHER THAN. Applied to process parameters to identify deviations from design intent in a HAZOP study.

PID controller equation

Output = K_c (e + (1/τ_I)∫e dt + τ_D de/dt). Proportional, integral, derivative control. K_c is gain, τ_I integral time, τ_D derivative time.

Limiting reactant

Reactant completely consumed in a chemical reaction. Determines maximum product yield. Other reactants are in excess. Identified by comparing stoichiometric ratios.

Percent excess

(moles supplied − moles stoichiometric)/moles stoichiometric × 100. For a reactant not limiting. Used in combustion calculations to specify air excess.

Extent of reaction

ξ (xi): n_i = n_i0 + ν_i ξ. ν_i is stoichiometric coefficient (positive for products, negative for reactants). Measures progress of reaction.

Galvanic corrosion

Accelerated corrosion when two dissimilar metals are electrically coupled in an electrolyte. More active metal (anode) corrodes faster; more noble metal (cathode) is protected.

PREN

Pitting resistance equivalent number = %Cr + 3.3%Mo + 16%N. Ranks stainless steels by resistance to pitting corrosion. Higher PREN indicates better resistance.

Cathodic protection

Technique to control corrosion by making metal the cathode of a cell. Uses sacrificial anode (more active metal) or impressed current. Protects pipelines, tanks, ship hulls.

Gaussian plume model

C(x,y,z) = (Q/(2πuσ_yσ_z)) exp(−y²/(2σ_y²)) [exp(−(z−H)²/(2σ_z²)) + exp(−(z+H)²/(2σ_z²))]. Predicts downwind pollutant concentration from continuous point source.

BOD5

Biochemical oxygen demand over 5 days at 20°C. Measures biodegradable organic matter in water. Used to assess wastewater strength and treatment efficiency.

Activated sludge F/M

Food-to-microorganism ratio = Q S0/(V X). Q is influent flow, S0 influent substrate, V aeration tank volume, X biomass concentration. Controls sludge bulking and treatment performance.

API gravity

API = (141.5/SG) − 131.5. Inverse measure of crude oil density. Higher API means lighter crude. Sweet crude has low sulfur (<0.5%), sour has high sulfur.

Octane number

Measure of gasoline antiknock quality. Iso-octane = 100, n-heptane = 0. Higher octane resists knocking. Cetane number is analogous for diesel fuel (hexadecane = 100).

FCC regenerator

Burns coke deposited on zeolite catalyst in fluid catalytic cracking. Restores catalyst activity. Provides heat for cracking reactions. Coke + O2 → CO2 + H2O.

Polydispersity index

PDI = M_w/M_n. Ratio of weight-average to number-average molecular weight. Measures breadth of molecular weight distribution. PDI = 1 for monodisperse polymer.

Carothers equation

X_n = 1/(1−p) for stoichiometric step-growth polymerization. X_n is number-average degree of polymerization, p is extent of reaction. High X_n requires p > 0.99.

Glass transition temperature

T_g: temperature below which amorphous polymer is glassy and brittle, above which it is rubbery. Depends on chain stiffness, crosslinking, and crystallinity. Not a phase transition.

Michaelis-Menten equation

v = V_max S/(K_m + S). Enzyme kinetics rate law. K_m is substrate concentration at half maximum velocity. V_max is maximum rate at saturating substrate.

Monod growth kinetics

μ = μ_max S/(K_s + S). Specific growth rate of microorganisms. K_s is half-saturation constant. Analogous to Michaelis-Menten equation for enzyme kinetics.

Chemostat steady state

At steady state, specific growth rate μ equals dilution rate D = F/V. Biomass concentration X = Y_X/S (S0 − S). Used for continuous culture studies.