Stoichiometry mole ratio study lab

Chemistry 151 College of the Canyons Week 8 – Reaction Stoichiometry Fall 2020 Name __________________________________ Date ____________________________ Section_________________________________ INTRODUCTION When a chemical reaction occurs, reactants are converted to products. The quantitative relationship between the reactants and products is termed stoichiometry. Because matter is not created or destroyed in a chemical reaction, the number of atoms of each element should be balanced on each side of the reaction. To do this, we use stoichiometric coefficients. Stoichiometric coefficients are the numbers placed in front of atoms, ions, or molecules in a chemical equation. Stoichiometric coefficients establish the mole ratio between reactants and products in a chemical reaction. For example, in this reaction: N2(g) + 3 H2(g) 2 NH3(g) The mole ratios between the molecules are: 1 mol N2 : 3 mol H2 : 2 mol NH3 The mole ratio means that 1 mol of N2 will react with 3 mol of H2 to form 2 mol of NH3. The mole ratio is used to compare the amount of reactants needed for the reaction to occur, the amount of products formed in the reaction, or to convert amounts of reactants to products. The stoichiometric coefficient and resulting mol:mol ratios of chemical reactions are essential to solving quantitative problems based on chemical reactions. Example #1– How many moles of NH3(g) can be produced from 2.62 moles of N2(g)? 2.62 𝑚𝑚𝑚𝑚𝑚𝑚 𝑁𝑁2 ∗ 2 𝑚𝑚𝑚𝑚𝑚𝑚 𝑁𝑁𝑁𝑁3 = 𝟓𝟓. 𝟐𝟐𝟐𝟐 𝒎𝒎𝒎𝒎𝒎𝒎 𝑵𝑵𝑵𝑵𝟑𝟑 1 𝑚𝑚𝑚𝑚𝑚𝑚 𝑁𝑁2 While the mol:mol ratio provides information on different reactants or products in a chemical reaction, to calculate measurable data in the laboratory, the units must be in grams. From our prior experiments, we know that to convert from moles to grams, or vice versa, we must use the molar mass. For a general stoichiometric calculation, the scheme below can be used as a guide. In this example, ‘A’ represents the product or reactant we know something about and ‘B’ represents the product or reactant we want to know something about. grams A moles A moles B Scheme 8.1 – The Relationship between Stoichiometric Coefficients Page 1 grams B Chemistry 151 College of the Canyons Week 8 – Reaction Stoichiometry Fall 2020 Example #2 – How many grams of NH3 can be produced from the reaction of 1.32 grams of H2? 𝑁𝑁2 (𝑔𝑔) + 3𝑁𝑁2 (𝑔𝑔) → 2𝑁𝑁𝑁𝑁3 (𝑔𝑔) A B Grams H2 1.32 𝑔𝑔 𝑁𝑁2 ∗ Moles H2 Moles NH3 Grams NH3 1 𝑚𝑚𝑚𝑚𝑚𝑚 𝑁𝑁2 2 𝑚𝑚𝑚𝑚𝑚𝑚 𝑁𝑁𝑁𝑁3 17.04 𝑔𝑔 𝑁𝑁𝑁𝑁3 ∗ ∗ = 7.42 g NH3 2.02 𝑔𝑔 𝑁𝑁2 3 𝑚𝑚𝑚𝑚𝑚𝑚 𝑁𝑁2 1 𝑚𝑚𝑚𝑚𝑚𝑚 𝑁𝑁𝑁𝑁3 In most chemical reactions, one of the reactants will run out first. For example, if you wanted to make peanut butter and jelly sandwiches, you may go to the store and buy a jar of peanut butter, a jar of jelly and a loaf of bread. To assemble the sandwiches (the product), you would use the following ‘reaction’