Basic Concepts in Chemical Engineering

Question 1

Thermodynamic Equilibrium

Answer 1

state of a non-reactive system
-mechanical equilibrium (no net driving force for momentum)
-thermal equilibrium (no net driving force for heat)
-diffusional equilibrium (no net driving force for molecular diffusion/mass)

Question 2

Chemical Equilibrium

Answer 2

-concentrations of reactants and products stop changing wrt time (in addition to temperature and pressure being the same throughout).
-forward/reverse reactions proceed at the same rate (not zero)

Question 3

When is Gibbs free energy at a minimum?

Answer 3

under chemical equilibrium at a specified temperature and pressure with no external forces, Gibbs free energy is at a minimum

Question 4

Formula for Gibbs Energy

Answer 4

dG = sum (j=1 to m) Uj dNj = 0 (at minimum)
-Uj s the chemical potential of molecular species j
-Nj is the amount of molecular species j

Question 5

The minimization of Gibbs Free Energy is a standard optimization problem known as ______

Answer 5

Constrained minimization

Question 6

Zeroth Law of Thermodynamics

Answer 6

If two bodies are in thermal equilibrium with a third body, then they are also in thermal equilibrium with each other.
-if A=B, C=B, then A=C

Question 7

First Law of Thermodynamics

Answer 7

Energy can be neither created nor destroyed. It can change forms. “Conservation of Energy”
“Interconvertibility of Energy”

Question 8

Second Law of Thermodynamics

Answer 8

The entropy of an isolated system, not in equilibrium will tend to increase over time, approaching a maximum at equilibrium.
“Order vs Disorder”
“Hierarchy of Energy forms”
(heat flows from hot to cold)

Question 9

Third Law of Thermodynamics

Answer 9

As temperature approaches absolute zero, the entropy of a system approaches a constant minimum.

Question 10

Bernoulli’s Principle

Answer 10

Increase in the speed of a fluid occurs simultaneously with a decrease in static pressure and/or decrease in the fluid’s potential energy. It applies to isentropic flows (no friction, no work, no heat terms)

Question 11

Darcy-Weisbach Equation

Answer 11

Δp/L = Fd (p/2)(u^2/D)
For laminar flow Fd = 16/Re
For turbulent flow Fd from Darcy’s friction factor chart (fanning friction factor)
-Friction/Viscous Head loss

Question 12

Navier Stokes Momentum Equation

Answer 12

p(Du/Dt) = -∇p +u∇^2u+(1/3)u∇(∇.u) +pg

Question 13

Three modes of heat transfer

Answer 13

conduction, convection, radiation

Question 14

One-Dimensional Energy Balance (with Conduction)

Answer 14

∂/∂x (k ∂T/∂x) + q = 1/α (∂T/∂t)

Question 15

Fourier’s Law of Heat Conduction

Answer 15

qx = -kA (dT/dx)

Question 16

Newton’s Law of Heat Convection

Answer 16

q = hA|ΔT|

Question 17

Radiation (net) Heat Transfer

Answer 17

q12 = δ A1F12 (T1^4-T2^4)

Question 18

Fick’s First Law

Answer 18

It is analogous to Darcy’s Law (Fluid Flow), Ohm’s law (electrical charge transport), and Fourier’s law (heat transport). Molar flux: j = -D (dc/dx)

Question 19

Molar Flux Formula

Answer 19

j = -D (dc/dx)

Question 20

Analogous transport properties for the three transfer properties (variables)

Answer 20

v (momentum diffusivity)
α (thermal diffusivity)
D (molecular diffusivity)

Question 21

Fick’s Second Law

Answer 21

Concentration variation with respect to time
∂C/∂t = D ∂^2C/∂x^2

Question 22

Convection Mass Transfer (flux)

Answer 22

Na = k|ΔCa|