Chapter 12: Stoichiometry

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Chapter 12 Stoichiometry
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Stoichiometry

• Stoichiometry The calculations of quantities of
  substances involved in chemical reactions.

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Coefficients

• Coefficients in a balanced reaction show the MOLE
  TO MOLE RATIO.
• Ex. 1N2 3H2 ? 2NH3
• There is a 132 mole ratio
• Note Dont use coefficients when adding up the
  mass!

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Mole-Mole Conversions

• 2A B ? 3C 7D
• Given the number of moles of reactant A (6
  moles), you can find
• The of moles of B needed to react completely
  with 6 moles of A.
• 2) The of moles of product C formed.
• 3) The of moles of product D formed.

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Mole to Mole Example

• N2 3H2 ? 2NH3
• If you have 2 moles of N2, how many moles of NH3
  will be produced?

2 mol N2
mol NH3 mol N2
2 1
2 x 2 / 1 4 moles NH3
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Mole to Mole Example

• N2 3H2 ? 2NH3
• If you want 5 moles of product, how many moles of
  hydrogen gas do you need?

5 mol NH3
mol H2 mol NH3
3 2
5 x 3 / 2 7.5 moles H2
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Mole to Mole Example

• N2 3H2 ? 2NH3
• How many moles of nitrogen are needed to react
  completely with 8 moles of hydrogen?

8 mol H2 1 mole N2 3 mole
H2 8 x 1 / 3 2.67 mole N2
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Reaction Conversions

• The only way to convert from one compound to
  something totally different in the reaction is to
  use the MOLE TO MOLE RATIO from the
  coefficients!!!

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Reaction Conversions

• Note If you dont have moles already, your
  first step is to convert to moles!
• Mole Review

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Mole Map
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Mass-Mass Conversions

• N2 3H2 ? 2NH3
• How many grams of hydrogen gas are required for
  3.75g of nitrogen gas to react completely?

grams N2 ? mole N2 ? mole H2 ? grams H2
3.75 gN2
1 mole N2 28 g N2
3 moles H2 1 mole N2
2 g H2 1 mole H2
3.75 x 3 x 2 / 28
0.80 g H2
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More Mass-Mass Conversions

• N2 3H2 ? 2NH3
• How many grams of H2 are required to produce 5.0
  grams of NH3?

Grams NH3 ? moles NH3 ? moles H2 ? grams H2
5.0 g NH3 1 mole NH3 3 mole H2 2 g
H2 17 g NH3 2 mole
NH3 1 mole H2
5.0 x 3 x 2 / 17 / 2 0.88 g H2
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Mass Volume Conversions

• C2H4 3O2 ? 2H2O 2CO2
• How many liters of CO2 (at STP) would be produced
  from the combustion of 4.0 grams of C2H4?

grams C2H4 ? moles C2H4 ? moles CO2 ? liters CO2
4.0 g C2H4
1 mole C2H4 28 g C2H4
2 moles CO2 1 mole C2H4
22.4 L CO2 1 mole CO2
4.0 x 2 x 22.4 / 28
6.4 L CO2
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More Mass-Volume Conversions

• C2H4 3O2 ? 2H2O 2CO2
• How many liters of O2 would be needed to produce
  6.8 grams of H2O?

grams H2O ? moles H2O ? moles O2 ? liters O2
6.8 g H2O 1 mole H2O 3 moles O2 22.4 L
O2 18 g H2O 2 moles H2O 1
mole O2
6.8 x 3 x 22.4 / 18 / 2 12.7 L O2
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Volume Volume Conversions

• N2 3H2 ? 2NH3
• How many liters of ammonia (NH3) would be
  produced from 8.0 liters of hydrogen?

liters H2 ? moles H2 ? moles NH3 ? liters NH3
8.0 L H2
1 mole H2 22.4 L H2
2 moles NH3 3 moles H2
22.4 L NH3 1 mole NH3
8.0 x 2 x 22.4 / 22.4 / 3
5.33 L NH3
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More Volume-Volume Conversions

• N2 3H2 ? 2NH3
• How many liters of N2 would be needed to produce
  15.0 liters of NH3?

liters NH3 ? moles NH3 ? moles N2 ? liters N2
15.0 L NH3 1 mole NH3 1 mole N2 22.4
L N2 22.4 L NH3 2 moles NH3 1
mole N2
15 x 22.4 / 22.4 / 2 7.5 L N2