Download Covenant Home Curriculum® Tenth Grade Sample Page 1 Science

Science sample from Exploring Creation With Chemistry
Module #5: Counting Molecules and Atoms in Chemical Equations
155
Let’s do one more problem just to make sure you really understand how to use the coefficients in a
chemical equation:
If a chemist has 0.234 moles of C2H6O, how many moles of carbon will the chemist get by decomposing the sample?
We are not given the chemical equation in this problem, but we can figure it out. The problem says
that the chemist is decomposing C2H6O. The chemical reaction, then, is:
C2H6O —> C + H6 + O2
Remember, both hydrogen and oxygen are homonuclear diatomics, but carbon is not. Thus, the chemical
formula for carbon is C, but the chemical formula for hydrogen is H6, and the chemical formula for oxygen
is O2. Balancing the equation gives us:
2C2H6O —> 4C + 6H2 + O2
This chemical equation tells us that 2 moles C2H6O will decompose into 4 moles of C. Thus,
2 moles C2H6O = 4 moles C
Now that we have our conversion relationship for this particular reaction, we can simply convert:
0.234 moles C2H6O
4 moles of C
X
1
=
0.468 moles of C
2 moles C2H6O
Our chemical equation, then, tells us that when 0.234 moles of C 2H6O decompose, they produce 0.468
moles of C. Once again, the numbers in the conversion relationship are exact, since they come from the
chemical equation. Therefore, the number of significant figures in the original measurement determines
the number of significant figures in the answer.
Hopefully you are beginning to appreciate the power behind the mole concept. It not only allows
us to count the number of atoms or molecules that exist in a sample of matter, but it also allows us to
predict the quantities of substances that are produced in a chemical reaction. See if you can perform the
latter of these two techniques:
ON YOUR OWN
5.10 A chemist obtains a 122.3-mole sample of ammonia (NH3). If the chemist allows this sample to
decompose, how many moles of hydrogen gas will be produced?
Covenant Home Curriculum® Tenth Grade Sample
Page 1
Science sample from Exploring Creation With Chemistry
Module #5: Counting Molecules and Atoms in Chemical Equations
Covenant Home Curriculum® Tenth Grade Sample
156
Page 2