Chemistry Reference
In-Depth Information
The trick to solve this problem is to look at the coefficients in front of
each of the substances in the reaction. These coefficients give you the mo-
lar ratios that you need. For example, the fact that both water and carbon
dioxide have a “6” in front means that the same number of moles of each
will be generated as the products of this reaction. The ratio 6:6 can be
reduced to 1:1, so if you produced 1 mole of water, you would produce 1
mole of carbon dioxide. If you produced 1.56 moles of water, you would
produce 1.56 moles of carbon dioxide.
This question isn't about the products of the reaction, so I will cross them
out. It asks about the reactants, the glucose and oxygen. The coefficients in
front of these substances tell us that the ratio of glucose to oxygen is 1:6. This
means that if we wanted to react 1 mole of glucose, we need 6 moles of
oxygen. If we wanted to react 2 moles of glucose, we would need 12 moles of
oxygen. If we want to react 3 moles of glucose, we would need 18 moles of
oxygen. Look how we can use a simple ratio to solve these problems.
C
6
H
12
O
6
+ 6O
2
6H
2
O + 6CO
2
glucose + oxygen
water + carbon dioxide
glucose
oxygen
coefficients
1
3
6
x
=
# of moles
Now, cross-multiplying, we get x = 3 × 6 = 18. So, it takes 18 moles of
oxygen to react completely with 3 moles of glucose.
Let's use the same chemical reaction and figure out how many moles
of oxygen it would take to react completely with 0.25 moles of glucose.
You may not be ready to do this example in your head, but it is easy enough
when you use the ratio.
Example 2
How many moles of oxygen (O
2
) are required to react completely
with 0.25 moles of glucose (C
6
H
12
O
6
) according to the balanced
chemical equation shown here?
C
6
H
12
O
6
+ 6O
2
6H
2
O + 6CO
2
glucose + oxygen
water + carbon dioxide
glucose
oxygen
coefficients
1
0.25
6
x
=
# of moles
