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The first thing that we did in this problem solution was to read the problem statement. We obviously need to do this any time we are beginning to attack a new problem. After reading the problem statement, we always want to start trying to translate the problem statement that we are given into tools that we know how to use. These steps (that we almost always do) are listed on the right in red color and allow us to break the complex problem up into pieces that we can handle.
We almost always draw a flow sheet for a process so we have a visual representation of how pieces of equipment are connected. Once we draw the flow sheet, we start to organize the given information on it so we can have variables and knowns to work with. We also almost always make a table to keep track of our flowrates in. This table will be a nice place for organizing all the information that we're finding as we solve the problem so that we don't lose some important number on a sheet of scrap paper. We also almost always identify whatever we are trying to solve in terms of math variables so we can relate those to our table. This is done so we know when we can stop working on our problem and move on to something else.
In this case, we were told that a chemical reaction was happening in the problem statement. We realized at this point that problems with chemical reactions can almost never be solved unless you've written a balanced chemical reaction for all the reactions involved. This is also needed before you can write the extents of reaction equations that are almost always needed to solve for all the information around a reactor. The in-out+gen-cons=acc equation requires extent of reaction information from the balanced chemical reaction stoichiometric equations. With that said, we realized we need to use the labelled flowsheet and the balanced reaction to write the extent of reaction equations for all of the species involved in our reaction.
There are a few more steps that we'll always do in solving a problem and we'll certainly do in this case. These are also listed in red on the right. These steps are solving all equations and checking our final answers.
For problems without reactions, we don't need extents of reaction equations, but can rely on just an overall mass balance instead (since there are no reactions to worry about). In this problem, we can still use the overall mass balance to check our answer at the end of our solution to make sure that we haven't made any silly mistakes in math along the way. We'll come back to that in later pages and show you how to do that.
There were many steps that we didn't need to do in this problem that were listed on the original problem solution page. These steps are listed in color on the right. They include:
- Using the ideal gas law (to relate P, V, T, and n for an ideal gas).
- Using molecular weight (to relate mass flowrates to mole flowrates).
- Using density (to relate mass flowrates to volume flowrates).
- Using a manometer equation (to relate height, density, etc. to pressures).
- Using unit conversions first (to get numbers into the same units, like reconciling degrees Celsius with degrees Kelvin).
This still leaves us with choosing a basis. First let's replace our wordy picture next to this description with all the information we have and go to a new page.
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