Chemistry Reference
In-Depth Information
5.
How many dm
3
of hydrogen gas at STP will be produced from the
decomposition of 15.0 g of water?
6.
How many grams of oxygen will be produced from the decomposition
of enough water to generate 22.4 dm
3
of hydrogen gas at STP?
Complete all of the required steps to answer the following questions.
7.
How many dm
3
of oxygen at STP can react completely with 3.50 g of
magnesium in a synthesis reaction, which forms magnesium oxide?
8.
How many grams of water will form when 1.00 dm
3
of ethane at STP
reacts with an excess of oxygen in a combustion reaction?
Lesson 7-6: Volume-Volume Problems
At the end of Lesson 7-5, I mentioned a shortcut that I would teach
you for doing volume-volume problems. The shortcut is so logical and use-
ful that it would not make any sense to solve volume-volume problems
without it. However, there is a very real danger associated with learning
this shortcut. Some students learn the shortcut and then try to apply it to
mass-mass and mass-volume problems. Be warned: You cannot do this!
The shortcut only works for volume-volume problems, and trying to use it
on the other types of problems will result in the wrong answer!
To introduce the shortcut, I will solve the first volume-volume prob-
lem the long way. If you look at my work carefully, you should not only be
able to figure out what the shortcut is, but you should be able to under-
stand why it works for this—and only this—type of problem.
Volume-volume problems are used when you are only interested in
the gaseous components of a chemical reaction. The problems only give
you the volume of a substance and only ask for the volume of another sub-
stance. The following is an example of this type of problem.
Example 1
How many dm
3
of hydrogen gas are needed to react with exactly
30.0 dm
3
of oxygen, in order to synthesize water, assuming both
gases are at STP?
Well, we aren't given very much to start with, but it is easy enough to
complete Step 1, starting with a balanced equation based on our knowledge
of synthesis reactions from Lesson 6-2. Let's complete the first two steps.
