Calculating Mole Ratios
A _________________________is a name we give to a statement showing that______________________________ are
__________________________.
These two ratios are equal:
a:b
=
c:d
But, we can write this as a fraction:
𝑎
𝑏
=
𝑐
𝑑
Examples: Fill in the missing piece.
1.
4.
3
5
2
=
=
25
3
6
2.
5.
14
=
3
12
=
5
10
5
3.
6.
6
2
6
=
=
9
8
24
We can apply this same concept to mole ratios in reactions.
N2 + 3 H2  2 NH3
1. Use the above equation to answer the questions.
a. Write the ratio between N2 and H2 as a fraction:
_____________________________
b. Suppose you had 10 moles of N2, how many moles of H2 would you need?
_____________________________
c. How did you find the answer to (b) above? Explain.
d. Write the ratio between H2 and NH3 as a fraction:
_____________________________
e. Suppose you had 4 moles of NH3, how many moles of H2 would be needed?
_____________________________
f.
How did you find the answer to (e) above? Explain.
g. How could we use this process or method that you described in (c) and (f) to solve any problem? Explain.
We are going to use proportions to solve mole ratio problems.
2. Use this equation for the next set of problems:
8 H2 + S8  8 H2S
a. Write the molar ratio for S8 to H2S as a fraction:
b. How many moles of sulfur, S8, would you need to make 16.0 moles of H2S?
𝑥 𝑚𝑜𝑙 𝑆8
=
16.0 𝑚𝑜𝑙 𝐻2 𝑆
𝑚𝑜𝑙 𝑆8
𝑚𝑜𝑙 𝐻2 𝑆
c. Write the molar ratio for S8 to H2 as a fraction:
d. 4.0 moles of hydrogen, H2, are consumed in the reaction. How many moles of sulfur, S8, are also consumed?
𝑚𝑜𝑙 𝑆8
=
𝑚𝑜𝑙 𝐻2
𝑚𝑜𝑙 𝑆8
𝑚𝑜𝑙 𝐻2
3. Use this equation for the next set of problems:
2 H2 + O2  2 H2O
a. Write the molar ration for O2 to H2O as a fraction:
b. How many moles of oxygen, O2, are needed to produce 10.0 moles of water, H2O?
𝑚𝑜𝑙 𝑂2
=
𝑚𝑜𝑙 𝐻2 𝑂
𝑚𝑜𝑙 𝑂2
𝑚𝑜𝑙 𝐻2 𝑂
c. Write the molar ratio for H2 to O2 as a fraction:
d. How many moles of hydrogen, H2, are needed to react with 3.0 moles of oxygen, O2?
=
e. 12.0 moles of water, H2O, are produced. How many moles of hydrogen, H2, are needed?
f.
2.75 moles of hydrogen, H2, are reacted. How many moles of oxygen, O2, are needed to complete the reaction?