Note: Real exam questions from 2012, Knowledge section, Morning session, Question 43
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43. For a certain system, which of the following equations apply to the material balance for steady-state operation? A: Input material quantity = Output material quantityB: Input material quantity = Output material quantity + Accumulated material quantity
C: Input material quantity ± Material quantity consumed in the reaction = Output material quantity
D: Input material quantity ± Material quantity consumed in the reaction = Output material quantity + Accumulated material quantity
Should we choose AC or CD for this question? In steady-state operation, there should be no accumulated amount of material. However, some people say that the accumulated amount in D can be set to 0; is that reasoning also valid?
Definition of steady-state operation: Choose AC that does not change over time
43 Correct answer: AC. Since the problem states that a steady state has been reached, there are no cumulative terms left! As the cumulative term equals 0, if it appears in the formula, that means it cannot be zero. Remember to use causal reasoning when solving problems; one cannot rely on arbitrary assumptions!
Professional knowledge, Question 43 in the morning: http://bbs.hcbbs.com/thread-1301570-1-19.html and http://bbs.hcbbs.com/thread-1227010-1-23.html
A Input material quantity = Output material quantity. C Input material quantity ± Material quantity consumed in the reaction = Output material quantity