[http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH03/FG03_01.JPG]

Stoichiometry 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 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 Conversions 4 Na + O2  2 Na2O 8.0 mol Na 2 mol Na2O = 4.0 mol Na2O 4 mol Na Significant digits! Mole Ratio from balanced equation. Start with the quantity given to you in the problem.

Mass 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?

Mass to Mass Conversions 4 Na + O2  Na2O 2 92.0 g Na 1 mol Na 2 mol Na2O 62.0 g Na2O 23.0 g Na 4 mol Na 1 mol Na2O = 124 g Na2O

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  Al2O3 4 2 3 2

Other Variations…. Al + O2  Al2O3 4 3 2 54.0 g Al 1 mol Al 3 mol O2

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  MgO 2 2

Other Variations…. Mg + O2  MgO 2 2 4.00 mol O2 2 mol MgO 1 mol O2 6.02 x 1023 molec MgO 1 mol O2 1 mol MgO = 4.82 x 1024 molec MgO