Material Balance Without Reaction Questions and Answers

Answer: A

Correct answer: 37.5 moles per hour

Total and light-component balances together give the lever rule: \[ D = F\,\frac{x_F - x_B}{x_D - x_B} = 100\times\frac{0.40-0.10}{0.90-0.10} = 100\times\frac{0.30}{0.80} = 37.5\ \mathrm{mol/h}. \] The check is that the bottoms are then 62.5 mol/h, and \( 37.5\times0.9 + 62.5\times0.1 = 40 \), which is the light component fed.

Answer: B

Correct answer: True

An envelope may be drawn anywhere - around one unit, several, or the whole plant - and a valid balance follows for whatever streams cross it. That freedom is the main tool available: choosing an envelope that cuts few streams, or that excludes the units carrying the awkward unknowns, often gives the answer in one equation where a unit-by-unit march would take several.

Answer: C

Internal streams including recycles cancel out, so the overall balance is usually the simplest one available. It is normally written first and the unit balances then fill in the internal detail. Every recycle cancels within the plant envelope.

Answer: D

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason is the definition of the envelope. A recycle begins and ends inside the plant boundary, so it crosses that boundary nowhere and cannot appear in a balance written around it. This is why the overall balance is usually the easiest one in a recycle problem and why it is drawn first.

Answer: A

Correct answer: each tie their own phase together

With immiscible solvents each carrier stays entirely in its own phase, so its flow is the same entering and leaving. Each therefore serves as a tie component for its own stream, and the balances can be written on a solute-free basis - which reduces the problem to tracking the solute alone and is the standard simplification in extraction calculations.

Answer: B

The first two are correct and are basic discipline. The third invites exactly the confusion the labelling is meant to prevent, since two streams that happen to be equal must still be shown to be so. An equality is a result of the balance, not an assumption.

Answer: C

It has infinitely many solutions rather than none, and the remedy is to supply another specification. Recognising which case you are in is what the degrees of freedom count is for. One more specification collapses the family to a single answer.