Chemistry Reference
In-Depth Information
Now, cross-multiplying, we get x = 0.25 × 6 = 1.5. So, it takes 1.5 moles
of oxygen to react completely with 0.25 moles of glucose.
For our last example, let's try another chemical reaction.
Example 3
How many moles of water (H
2
O) can be produced from the
combustion of 5 moles of methane (CH
4
) according to the balanced
chemical reaction shown here?
CH
4
+ O
2
2H
2
O + CO
2
methane + oxygen
water + carbon dioxide
Here, the molar ratio given by the coefficient of methane and water is
1:2. This means that for every 1 mole of methane you burn, you produce 2
moles of water. You probably can see right away that if you burn 5 moles of
methane you will get 10 moles of water, but I will go through the formality
of showing the ratio, just in case.
CH
4
+ O
2
2H
2
O + CO
2
methane + oxygen
water + carbon dioxide
methane water
coefficients
1
5
2
x
=
# of moles
Now, cross-multiplying, we get x = 5 × 2 = 10. So, the combustion of 5
moles of methane will produce 10 moles of water.
Practice the following problems before moving on to Lesson 7-4.
Lesson 7-3 Review
Base your answers to questions 1-5 on the following balanced chemi-
cal equation.
C
3
H
8
+ 5O
2
4H
2
O + 3CO
2
propane + oxygen
water + carbon dioxide
1.
How many moles of propane would be required to react completely
with 10 moles of oxygen?
2.
How many moles of oxygen would be required to react completely
with 3 moles of propane?
3.
How many moles of water would be produced if 3 moles of propane
react with an excess of oxygen?
