Chapter 4

Question 1

What is the law of conservation of mass?

Answer 1

mass can neither be created no destroyed

Question 2

What is a mass balance or material balance?

Answer 2

Mass balance is a consideration of the input, output, and distribution of a substance between streams in a process or stage.

Question 3

What is a batch process?

Answer 3

the feed is charged (fed) into a vessel at the beginning of the process and the vessel contents are removed sometime later.
- no mass crosses the system boundaries between the time the feed is charged and the time the product is removed.

Question 4

What is a continuous process?

Answer 4

the inputs and outputs flow continuously throughout the duration of the process.
ex: pumping a mixture of liquids into a distillation column at a constant rate and steadily withdrawing a product streams from the top and bottom of the column

Question 5

What is an example of a batch process?

Answer 5

readily adding reactants to a tank and removing the products and unconsumed reactants somtime later when the system has come to equlibrium

Question 6

What is a semibatch process?

Answer 6

Any process that is neither batch nor continuous

Question 7

What is an example of a semi batch process?

Answer 7

Allow the contents of a pressurized gas container to escape to the atmopshere; slowly bend several liquids in a tank from which nothing is being withdrawn

Question 8

What does it mean for a process to be operating at a steady state?

Answer 8

if all the values in a process do not change with time, except possibly for minor fluctuations about constant mean values

Question 9

What does it mean if a process is operating at a transient or unsteady state?

Answer 9

when any process variables change with time

Question 10

Which process is typically unsteady state operations?

Answer 10

batch and semi batch

Question 11

Which process is either steady state or transient?

Answer 11

continuous process

Question 12

What is the general equation for a balance?

Answer 12

input + generation - output - consumption = accumulation?

Question 13

What is a differential balance?

Answer 13

balances that indicate what is happening in a system at an instant in time
- this balance is usually applied to a continuous process
- terms are typically a rate

Question 14

What is an integral balance?

Answer 14

balances that describe what happens between two instants of time
- terms in the equation are an amount (people, gSO2, barrels)
- balance is usually applied to a batch process

Question 15

What is the simplified equation for a continuous steady state process?

Answer 15

input + generation = output + consumption

Question 16

What is the accumulation equation for a batch process?

Answer 16

initial input + generation = final output + consumption

Question 17

What is the purpose of a flow chart?

Answer 17

using boxes and symbols to represent process units (reactors, mixers, separation units) and lines with arrows to represent inputs and outputs

Question 18

What is the first step for labeling a flow chart?

Answer 18

Write the values and units of all known stream variables at the locations of the streams on the chart

Question 19

What is the second step for labeling a flow chart?

Answer 19

Assign algebraic symbols to unknown stream variables and write these variable names and their associated units on the chart

Question 20

What is a degree of freedom analysis?

Answer 20

using a properly drawn flowchart to determine whether you have enough information to solve a given problem

Question 21

What is the method for a degree of freedom analysis?

Answer 21

Draw and completely label a flowchart, count the unknown variables on the chart, and then count the independent equations relating them, and then subtract the second number from the first.

ex: n unknowns - n independent equations