calculation of quantities in chemical reactions.

 Describes by Amedeo Avagadro.  1 mole = 6.022x10 23 molecules, atoms, formula units or ions.  1 mole = 22.4L of gas

 A balanced chemical equation can be interpreted in terms of different quantities:  numbers of atoms  Numbers of molecules  Moles  Mass  Volume

 a balanced equation indicates that the number and type of each atom that makes up reactants & products  Both the number and types of atoms are not changed in a reaction  Law of Conservation of Matter!

 Ammonia reaction: one molecule of nitrogen reacts with three molecules of hydrogen.  N 2(g) + 3H 2 (g) → 2 NH 3 (g)  Nitrogen and Hydrogen react in a 1:3:2 ratio of molecules.  So 10 molecules of nitrogen react with 30 molecules of Hydrogen to make 20 molecules of Ammonia.  take Avogadro’s number of Nitrogen molecules and make them react with three times Avogadro’s number of Hydrogen molecules.  This would be the same 1:3 ratio of molecules of reactants.  The reaction would form two times Avogadro’s number of ammonia molecules.

 take Avogadro’s number of Nitrogen molecules and make them react with three times Avogadro’s number of Hydrogen molecules.  This would be the same 1:3 ratio of molecules of reactants.  The reaction would form two times Avogadro’s number of ammonia molecules.  So 6.02x10 23 molecules of N react with 18.06x10 23 molecules of H 2 to make 12.04x molecules of NH 3

 A balanced chemical equation also tells you the number of moles of reactants and products.  The coefficients indicate the relative numbers of moles of reactants and products  NOW you can calculate the amounts of reactants and products.  For ammonia, one mole of N 2 reacts with three moles of H 2 to form two moles of Ammonia molecules.  N 2(g) + 3H 2 (g) → 2 NH 3 (g)  total number of moles of reactants does not equal the total number of moles of product.

 number and type of atoms does not change in a rxn.  total mass of the atoms does not change  The mass of 1 mol of N 2 (28.0 g) plus the mass of 3 mol of H 2 (6.0 g) equals the mass of 2 mol of NH 3 (34 g).  the total number of grams of reactants does equal the total number of grams of product

 Assume STP (unless stated otherwise)  Remember 1 mol of any gas at STP occupies a volume of 22.4 L.  N 2(g) + 3H 2 (g) → 2 NH 3 (g)  The equation indicates that 22.4 L of N 2 reacts with 67.2 L (3 × 22.4 L) of H 2.  This reaction forms 44.8 L (2 × 22.4 L) of NH 3.

 STP, we’ve seen it before  Stand for “Standard Temperature and Pressure”  Not commonly used on the Regents anymore.  Usually says the numbers, but if they don’t, where do you find them?

 Mass and atoms are conserved in every chemical reaction.  molecules, formula units, moles, and volumes are not necessarily conserved— although they may be.