Pittcon 2012 Presentation-4

8/2/2019 Pittcon 2012 Presentation-4

1/16

Use of checklists to help students

better prepare for exams

Enrique Arce-Medina

Escuela Superior de Ingeniera Qumica e industrias Extractivas

INSTITUTO POLITECNICO NACIONAL

MEXICO


2/16

Checklists

+ PBL

Can improve learning


3/16

Checklists help us to

Organize

Set priorities

Prevent worries


4/16

noYes15 Did you correctly do the conversion from moles to mass in all input and output

streams to check the mass balance?

noYes14 Did you take into account all the outputs, purge, product and by-products?

noYes13 Did you take into account any impurities (inert and diluents) in the inputs?

noYes12 Did you note any especial relationship between molar variables given in the data e.g.

what input terms in the mol balance are related to what parameters?

noYes11 Did you properly apply the fixed proportions principle?

noYes10 Did you use mol units in reaction calculations?

noYes9 Did you check if your reactions are properly balanced?

noYes8 Did you have a clear idea of your inputs and outputs?

noYes7 Did you labeled all your flows, including symbols and units on the given values?

noYes6 Did you draw a sketch or schematics of the process steps?

noYes5 Did you identify the process steps required to transform raw material to finished

products?

noYes4 Did you clearly define targets to review progress while implementing your action plan?

noYes3 Did you define an action plan?

noYes2 Did you establish the basis?

noYes1 Did you make serious efforts to read and understand the text?

Study preparation checklist while solving material balance problems


5/16

Checklist in solving mass balance problems

Material balance problems can be solved by listing and

solving a series of equations, or using a table.

Molar change

Moles fed

Mass fed

MC

MB

MA

Molar mass

CCBB+AA


6/16

Example 1

A mixture of hydrogen and nitrogen is fed to a

reactor, where they react to form ammonia (NH3).

The nitrogen flow rate into the reactor is 280 kg/min

and the hydrogen is fed at a rate of 60 kg/min. Of theH2 fed to the reactor, 50% is consumed by reaction.

What is the flow rate of N2, H2, and NH3 in the reactor

outlet?


7/16

Process diagram

Reactor

H2 (60 kg/min)H2 (?)

N2 (?)

NH3 (?)N2 (280 kg/min)

Basis: H2 fed to reactor

Reaction: H2 + 3 N2 2 NH3


8/16

2 NH3

3 H2

+N2

17228Molar Mass,iM

231Stoichiometric coefficients, i

060280Mass fed, kg/min0

iw

060/2=30280/28=10Moles fed, kmol/min ,

iii Mwn /00

=

30*0.5=15Moles H2 reacted, kmol/minxnn

HH*0

22=

(15/3)*2=10(15/3)*3=15(15/3)*1=5Molar change, kmol/min, ijji nn *)/(=

1030-15=1510-5=5Moles at reactor outlet,

kmol/min, iii nnn =0

10*17=17015*2=305*28=140Mass at reactor outlet,kg/min,

iii Mnw =

240Total mass flow in,

kg/min,00

iwW =


kg/min,i

wW =

Did you check if your reactions are properly balanced?Did you use mol units in reaction calculations?Did you note any relationship between molar variables given in the dataDid you properly apply the fixed proportions principleDid you take into account all the outputs

Did you check the mass balance


9/16

Example 2

Nitrogen and hydrogen are fed at a 1:3 molar ratio to a

reactor, where they react to form ammonia (NH3). 50% of the

H2 fed is converted to ammonia, and the reactor produces

170 kg/min NH3. Calculate the flow rate of N2, H2, and NH3 inthe reactor inlet and outlet?

Reactor

H2 (3*moles N2)H2 (?)

N2 (?)

NH3 (170 kg/min)

N2 (?)


10/16

2 NH3

3 H2

+N2

17228Molar Mass,iM

231Stoichiometric coefficients, i

170NH3 produced, kg/min 3NHw

170/17=10Moles NH3, produced

kmol/min333

/NHNHNH Mwn =

(10/2)*2=10(10/2)*3=15(10/2)*1=5Molar change, kmol/min

, ijji nn *)/(=

30/3=10Moles of N2 fed, kmol/min,3/00

22 HNnn =

1030-15=1510-5=5Moles at reactor outlet,kmol/min,


kg/min, 00iwW =


kg/min,i

wW =

Solution

15/0.5=30Moles H2 fed, kmol/minxnn HH /22

0=

iii nnn =0


11/16

As the examples show the checklist were meant toserve as an aid in accomplishing goals through a

set of guided questions.

Students own monitoring of their work help themto appreciate how concepts and principles fittogether for better understanding of what has to bedone while solving problems.


12/16

21%

42%

37%

not useful

somehow useful

very useful

32%

44%

24%

How useful was the checklist for you?

Girls Boys

Survey results


13/16

As the course progress it was observed thatstudents perform better, because they can checkby themselves how well are doing their job, by

knowing their goals.

We have found that common mistakes identified in

previous semesters can be converted intochecklists items for future tests.


14/16

When asking to students to write and use their own

checklist they show too much opposition.

Not all students were enthusiastic about adoptingthe checklists.

But


15/16

Conclusions

Two thirds of students stated that using thechecklists help them to learn better, get moreorganized and focus on what is important.

After two semesters of using the checklists thegrades remains almost at the same average, butthe number of students falling the course

decreased, compared with previous semesterswhen checklists were not used.


16/16

Thankyou

Pittcon 2012 Presentation-4

Documents