Chemical engineeringLesson 1 of 1 in the course Mass and energy balances

Mass Balances: Components, Reactions, and Reactor Models

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

A mass balance applies conservation of mass to a defined physical system. It helps engineers determine where material goes, including flows that may be difficult to measure directly.

Input is material entering the system; output is material leaving; and accumulation is the change in the amount held inside the boundary. Accumulation can be positive or negative. If more enters than leaves, material accumulates; if more leaves than enters, the amount stored decreases.

All flashcards

What does steady state mean in a mass balance?
The amount of material stored in the system does not change with time, so accumulation is zero.
How does a system boundary affect recycle accounting?
A recycle stream is internal to a boundary around the whole process, but may be an inlet or outlet for an individual unit.
What distinguishes a batch reactor from a CSTR during operation?
A batch reactor has no material inlet or outlet during reaction; a CSTR is an open, well-mixed system.
What is data reconciliation in process engineering?
Adjusting redundant measurements to produce a consistent set of data that satisfies balance constraints.
What is conserved for each element in an ordinary chemical reaction?
The number of atoms of that element; reactions rearrange atoms among species.

Quiz questions

  1. What does the steady-state assumption imply for accumulation in a mass balance?Answer: The amount stored in the system is constant, so accumulation is zero.
  2. Which description identifies a continuously stirred tank reactor (CSTR)?Answer: An open-flow system assumed to be well mixed.
  3. How can an ideal plug flow reactor be approximated using stirred tanks?Answer: As the limiting case of infinitely many stirred tanks in series.
  4. What is the purpose of industrial data validation and reconciliation?Answer: To adjust redundant measurements so they satisfy process balance constraints.
  5. At chemical equilibrium in a closed reversible reaction, what is true of the forward and reverse reaction rates?Answer: They balance, so concentrations remain constant in time.

Based on the Wikipedia article Mass balance, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.

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