a.k.a….having twice as much fun by doing twice as much math

8 H : 8 OImagine that paperclips are atoms and that we’re starting with an equal number of hydrogen atoms and oxygen atoms. For example:

Let’s assemble our paperclip atoms into paperclip molecules.

2H2 + O2 -> 2H2O

H2 O2

O2H2 H2O

The product molecules are made out of the available reactant molecules.

O2H2 H2O

Continue to convert reactants to products.

O2H2 H2O

Continue to convert reactants to products.

O2H2 H2O

Continue to convert reactants to products.

O2H2 H2O

The reaction stops after forming 4 water molecules because there aren’t any more hydrogen molecules to react.

The reaction was limited by the amount of hydrogen initially present. Therefore,

2 H2 + O2 2 H2O

O2H2

+

H2O

4 mol H2

4 mol O2

Step 1: Assume all of the hydrogen reacts and determine the number of moles of water that would be formed.

4 mol H2O

= 4 mol

8 mol H2O

Step 2: Assume all of the oxygen reacts and determine the number of moles of water that would be formed. = 8 mol

Q: How many grams of water will be formed?

Step 3: Multiply the smaller molar amount by the gfm of water to find the number of grams of water that will be formed.

A: 4 mol x 18.015 g/mol

72 g H2O

2 H2 + O2 2 H2O

For the reaction below, how many moles of water will be formed if 1.55 moles of hydrogen gas is allowed to react with 0.30 moles of oxygen gas?

What is the limiting reagent?

1.55 mol H2 1.55 mol H2O

0.30 mol O2 0.60 mol H2O

O2

Which reagent is in excess?

H2How many grams of H2O (gfm = 18.015 g/mol) will be formed from this reaction?

0.60 mol H2O x 18.015 g/mol = 10.8 g of H2O will form

For the reaction below, how many grams of water will be formed if 1.17 g of hydrogen gas is allowed to react with 7.35 g of oxygen gas?

What is the limiting reagent?

2 H2 + O2 2 H2O

g:

gfm:

mol:

1.17 g 7.35 g

2.016 g/mol 31.999 g/mol

0.58 mol

—— 0.23 mol

0.58 mol

0.46 mol

x 18.015 g/mol

8.29 g

How many grams of water will be formed? 8.29 g

And now for

something

slightly

different…

+ +

+

The Great Candy Caper!

Mission: To separate the bag of candy into three identical piles and thereby determine which type of candy is the limiting reactant.

Caution: If you eat any of the candy before telling me what the limiting reactant is, you will self-destruct.

The Great Candy Caper!

Mission: To separate the bag of candy into four identical piles and thereby determine which type of candy is the limiting reactant.

Caution: If you eat any of the candy before telling me what the limiting reactant is, you will self-destruct.

4 Al + 3O2 2Al2O3 3H2 + N2 2NH3

CH4 + 2O2 CO2 + 2H2O CH2O + O2 CO2 + H2O

2 Al + 3 PbCl2 2AlCl3 + 3Pb Zn + 2HCl ZnCl2 + H2

1.08 g Al11.12 g PbCl2 2.92 g HCl

5.23 g Zn

9.60 g O2

18.02 g CH2O

1.28 g O2

2.16 g Al11.20 g N2

0.81 g H2

6.40 g O2

6.42 g CH4

2.72 g Al2O3

4.40 g CO2

3.55 g AlCl3

4.53 g NH3

5.40 g H2O

0.081 g H2