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StoichiometryStoichiometry

This is the study of quantities, or measurable relationships, that exist in chemical reactions.

The coefficients in balanced chemical equations always refer to the moles of chemicals that are needed.

Moles to Moles ConversionsMoles to Moles Conversions

Example: Na + O2 Na2O If you start with 8.0 moles of Na, how

many moles of Na2O will you have when the reaction is complete?

4 2

Moles to Moles ConversionsMoles to Moles Conversions

Start with the quantity given to you in the problem.

Significant digits!

Mole Ratio from balanced equation.

8.0 mol Na 2 mol Na2O

4 mol Na= 4.0 mol Na2O

4 Na + O2 2 Na2O

Mass to Mass ConversionsMass to Mass Conversions

Example: (Using same reaction…) If you start with 92.0 g of Na, how

many grams of Na2O will you have at the end of the reaction?

23.0 g Na

Mass to Mass ConversionsMass to Mass Conversions

92.0 g Na 1 mol Na 2 mol Na2O

4 mol Na 1 mol Na2O

62.0 g Na2O

= 124 g Na2O

Na + O2 Na2O4 2

Other Variations….Other Variations….

Example: If you start with 54.0 g of Aluminum,

how many moles of Oxygen do you need for the reaction to work completely?

Al + O2 Al2O32 234

27.0 g Al

Other Variations….Other Variations….

54.0 g Al 1 mol Al 3 mol O2

4 mol Al= 1.50 mol

O2

4 23Al + O2 Al2O3

Other Variations….Other Variations….

Example: If you start with 4.00 moles of

Oxygen, how many molecules of Magnesium Oxide will you have at the end of the reaction?

Mg + O2 MgO2 2

1 mol O2

Other Variations….Other Variations….

4.00 mol O2 2 mol MgO 6.02 x 1023 molec MgO

1 mol MgO

= 4.82 x 1024 molec MgO

2 2Mg + O2 MgO