Stoichiometry Stoichiometry Stoichiometry is the study of the mass relationships of the reactants and the products in a chemical reaction. How much stuff it takes to make a certain amount of new stuff. Based on the law of conservation of mass Mass of the reactants must equal the mass the products CH3OH(g) + O2(g) CO2(g) + H2O(g) Chemical reactions are mole ratios between the reactants and the products – not a mass ratio! Mole ratio – the ratio of moles of any two substances in a chemical reaction 2CH3OH(l) + 3O2(g) 2CO2(g) + 4H2O(g) 2 mol CH3OH : 2 mol CO2 3 mol O2 : 4 mol H2O There is not a direct relationship between masses of individual reactants and products. Must use the mole ratio to convert! R1 + R2 → P1 + P2 grams molar mass R1 moles R1 grams molar mass P2 moles P2 moles R1 (mole ratio) moles P2 Guidelines for Stoichiometry 1. 2. 3. 4. Write a balanced equation for the chemical reaction. Convert grams A to moles of A using the molar mass. Convert moles of A to moles of B using the mole ratio. Convert moles of B to grams of B using the molar mass. 3. Examples 24. Sulfuric acid reacts with sodium hydroxide to form sodium sulfate and water. How many grams of Na2SO4 are produced from 25.0 g of H2SO4? 25. In the reaction from #24, I need 550.0 g Na2SO4. What mass of each reactant is required? 26. How much oxygen will be required to react with 100.0 g KCl to produce KClO3. 27. What mass of hydrogen peroxide must decompose to produce 0.77 g of water? The other product is oxygen gas. 28. Space vehicles use solid lithium hydroxide to remove exhaled carbon dioxide according to the equation: LiOH + CO2 Li2CO3 + H2O. Determine the mass of carbon dioxide removed if the space vehicle carries 1.00 kg of LiOH. 29. How many grams of carbon dioxide are produced when 2.50 g of baking soda react with excess citric acid (H3C6H5O7) to produce Na3C6H5O7, carbon dioxide, and water. 30. Aspirin (C9H8O4) is produced when salicylic acid (C7H6O3) reacts with acetic anhydride (C4H6O3) according to the equation C7H6O3 + C4H6O3 C9H8O4 + HC2H3O2. Determine the mass of aspirin produced when 150.0 g of salicylic acid reacts with an excess of acetic anhydride.