lecture 5 - stoichiometry for constant volume systems (1)

7/21/2019 Lecture 5 - Stoichiometry for Constant Volume Systems (1)

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Lecture 5Stoichiometry, Liquid Systems

(constant volume systems)

Fall 2015

CHE 314

Chemical Reaction Engineering

1 Slides adapted from Fogler’s PowerPoint slides



2

• Recap algorithm to get reaction rate as a

function of conversion

• Stoichiometric table for constant volume batch

reactors

• Stoichiometric table for flow reactors with

constant volumetric flow rate.

Outline:



Algorithm

( )i A C gr =−Step 1: Rate Law

( ) ( ) X hC i =Step 2: Stoichiometry

( ) X f r A =−Step 3: Combine to get

How to find ( ) X f r A =−



Stoichiometry

We shall set up Stoichiometric tables using

species A as our basis of calculation (i.e. assume A

is the limiting reactant).

We will use the stoichiometric tables to express theconcentration as a function of conversion.

We will combine Ci = f(X) with the appropriate rate

law to obtain -r A = f(X).

Da

d C

a

cB

a

bA +→+



Batch System – Stoichiometric Table 1)

t = 0

NA0

NB0

NC0

ND0

NI0

t = t NA

NB

NC

ND

NI

Batch reactor

5

Da

d C

a

cB

a

bA +→+




6

Species Symbol Initial Change Remaining

B B N B0=N A0ΘB -b/aN A0X N B=N A0( ΘB-b/aX)

A A N A0 -N A0X N A=N A0(1-X)

Inert I N I0=N A0ΘI ---------- N I =N A0ΘI

N T0 N T =N T0+δN A0X

Where:0

0

0

0

00

00

0

0

A

i

A

i

A

i

A

ii

y

y

C

C

V C

V C

N

N ====Θ 1−−+=

a

b

a

c

a

d δ and

C C N C0=N A0ΘC +c/aN A0X N C =N A0( ΘC +c/aX)

D D N D0=N A0ΘD +d/aN A0X N D=N A0( ΘD+d/aX)

δ = change in total number of moles per mol A reacted




• If the reaction occurs in the liquid phase

• If a gas phase reaction occurs in a rigid (e.g. steel)

batch reactor

V =V 0

Then

C A= N

A

V

= N

A 0 1− X ( )V 0

= C A 0 1− X ( )

C B= N

B

V = N

A 0

V 0

Θ B− b

a X

= C

A 0Θ

B− b

a X

etc.

Constant Volume System



Batch System – rate as a function of X

Suppose −r A = k AC A2C B

Batch (constant volume): 0

V V =

( )

−Θ−=− X

ab X C k r B A A A

230 1

−r A = f X ( )we have

Ar −1

X



Practice Problem 1 - Batch System

Consider the following elementary reaction with

KC=20 dm

3

/mol and C A0=0.2 mol/dm

3

.

The reaction takes place in a constant volume

batch reactor.

Calculate the equilibrium conversion for gasphase reaction, Xe .

BA2 ⇔



Flow System – Stoichiometric Table 1)

entering

FA0

FB0

FC0

FD0

FI0

Leaving

FA

FB FC

FD

FI

Continuous-flow

reactor

Da

d C

a

cB

a

bA +→+



Flow System – Stoichiometric Table 2)

11

Species Symbol Initial Change Remaining

B B F B0=F A0ΘB -b/aF A0X F B=F A0( ΘB-b/aX)

A A F A0 -F A0X F A=F A0(1-X)

Inert I F I0=F A0ΘI ---------- F I =F A0ΘI

F T0 F T =F T0+δF A0X

Where:0

0

0

0

00

00

0

0

A

i

A

i

A

i

A

ii

y

y

C

C

vC

vC

F

F ====Θ 1−−+=

a

b

a

c

a

d δ and

C C F C0=F A0ΘC +c/aF A0X F C =F A0( ΘC +c/aX)

D D F D0=F A0ΘD +d/aF A0X N D=F A0( ΘD+d/aX)

δ = change in total number of moles per mol A reacted



Practice Problem 2 - Flow System liquid)

Consider the following elementary reaction with

KC= 10 dm3/mol and C A0 = CB0 = 2 mol/dm3.

The reaction takes place in a flow reactor.

Calculate the equilibrium conversion and

concentrations for the liquid phase reaction

below .

C B A ⇔+

lecture 5 - stoichiometry for constant volume systems (1)

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