Reaction Stoichiometry

  Deals with the mass relationships that exist between reactants and product  In this type of chemistry, a quantity is given, and based on the chemical formula, a calculation of an unknown is completed.  Problem types fall into four different categories Reaction Stoichiometry

  A given amount in moles and an unknown amount in mole  Mole known → mole unknown Reaction Stoichiometry

  A given amount in moles and an unknown amount in grams  Mole known → mole unknown → gram unknown Reaction Stoichiometry

  A given amount in grams and an unknown amount in moles  Gram known → mole known → mole unknown Reaction Stoichiometry

  A given amount in grams and an unknown amount in grams  Gram known → mole known → mole unknown → gram unknown Reaction Stoichiometry

  The conversion factor used to relate the number of grams of a substance to the number of moles of the substance  Always derived from the periodic table  Example: g Al 2 O 3 or 1Mole Al 2 O 3 1 Mole Al 2 O g Al 2 O 3 Molar Mass

  How much of a compound by mass is a particular element? Percent Composition

  What percent by mass is hydrogen in water? Sample Question

  What is the percent composition of the elements in Cu 3 (PO 4 ) 2 ? Sample Question

  When chemists discover new compounds in the laboratory they need to be able to determine the chemical formula of the compound in order to replicate it.  They first discover the simplest whole number ratio of atoms in the compound  This is known as the empirical formula  From this they derive the actual formula of the compound  This is known as the molecular formula Determining Chemical Formulas

  This can be derived knowing either the percent of each element in a compound or the number of grams used of each element.  Percent to Mass  Mass to Mole  Divide by Small  Multiply till Whole Determining the Empirical Formula

  A compound consists of 25.94% N and % O; what is its empirical formula? Determining the Empirical Formula

  A white solid consists of Na, S, and O. 32.4% is Na, and 22.6% is S, what is the compounds empirical formula? Determining the Empirical Formula

  A scientist formed a compound out of only tin and chlorine and it weighed 2.57 g. He knew he used 1.17 g of tin. Can you help him find the empirical formula? Determining the Empirical Formula

  Any multiple of a compounds empirical formula may or may not be a correct molecular formula.  For example C 2 H 4 and C 3 H 6 both have the same ratio of Carbon to Hydrogen (3:1), however, the substances are completely different. Molecular Formula

  By dividing the molecular mass by the mass of the empirical formula, we can obtain the multiple by which the molecular formula can be found. Calculating Molecular Formulas

  A compound has an empirical formula of CH 2 O and a molar mass of 180 g / mol, what is the molecular formula of the compound? Finding Molecular Formulas

  A compound has an empirical formula of NO2 and a molar mass of g/mol. What is its molecular formula? Finding Molecular Formulas

  A compound contains 0.70 g Cr, 0.65 g S, and 1.30 g O, the molar mass of the molecule is g/mol. What is the molecular formula?  Practice: do 39 p 237, and 158 p. 929 Finding Molecular Formulas

  A conversion factor that relates any two substances in a chemical reaction  This information comes directly from the balanced chemical equation Mole Ratio

  Ideal = all of the reactants are converted into products and we are not concerned about any other reactants left over  Usually the question will say one of the reactant is in excess Ideal Stoichiometry

  In the formation of water, how many moles of O 2 must react with 2 moles of H 2 ? Stoichiometry

  How many moles of H 2 O will be produced by the reaction of 10 grams of H 2 reacting with excess O 2 ? Stoichiometry

  How many moles of NH 3 will be produced from 3.8 moles of N 2 reacting with excess H 2 according to the following equation: N 2 + 3H 2 → 2NH 3 Stoichiometry

 N 2 + 3H 2 → 2NH 3  Using the same equation starting with 15.9 grams of nitrogen, how many moles of H 2 are required to completely react with the N 2 ? Stoichiometry

 N 2 + 3H 2 → 2NH 3  How many grams of NH 3 will be produced if we start with 350 g of H 2 ? Stoichiometry

  The limiting reactant is the reactant that limits the amount of the other reactant and the amount of product that can form in a chemical reaction. Limiting Reactants

 C + O 2 → CO 2 1 mole of Carbon reacts with 1 mole of O 2 to yield 1 mole of CO 2 or 5 mole of Carbon reacts with 5 mole of O 2 to yield 5 mole of CO 2 But what if you started with 5 moles of Carbon and 10 moles of O 2 ? Limiting Reactant

 C + O 2 → CO 2  The 5 moles of Carbon with react with the first 5 moles of O 2 to yield 5 moles of CO 2 ….but 5 moles of O 2 would be left over.  If there was more Carbon to start with, more CO 2 could have been formed.  Carbon in this case is a limiting reactant. Limiting Reactant

 N 2 H 4 + 2H 2 O 2 → N 2 + 4H 2 O If 0.75 moles of N 2 H 4 is mixed with 0.50 moles of H 2 O 2, what is the limiting reactant? How much of the excess reactant remains unchanged? How much of each product is formed, in moles? Limiting Reactant

Carbon reacts with steam to produce hydrogen and carbon monoxide. a.Write a balanced chemical equation for the reaction. b.If 2.40 moles of Carbon are exposed to 3.10 moles of steam, identify the limiting reactant. c.How many moles of each product are formed? d.What mass of each product is formed?

3Fe + 4H 2 O → Fe 3 O 4 + 4H 2 a.When 36.0g of H 2 O is mixed with 167g of Fe, which is the limiting reactant? b.What is the mass, in grams, of the Iron Oxide produced? c.What is the mass, in grams, of the excess reactant that remains when the reaction is completed?

  The theoretical yield is the maximum amount of product that can be produced from a given amount of reactant.  The measured amount of product obtained from a reaction is called the actual yield of that product. Percent Yield

  In most reactions, the actual product is less than the theoretical product.  This is due to side reactions or impurities in the product which must be removed. Percent Yield

  The percent yield is the ratio of the actual yield to the theoretical yield, multiplied by 100. Percent Yield