11.2 Stoichiometric Calculations Discovery School Ashley Lardizabal Ch 11 Stoichiometry 11.2 Stoichiometric Calculations Discovery School Ashley Lardizabal

OBJECTIVES Explain the sequence of steps used in solving stoichiometric problems. Use the steps to solve stoichiometric problems

Stoichiometric Calculations Need to obtain a certain amount of product from a reaction. Need to know how much product will be formed if a certain amount of reactant is used.

Using Stoichiometry STOICHIOMETRY is the study of quantitative relationships between the amounts of reactants used and the amount of products formed by the chemical reaction. Begin with a balanced chemical equation Mole ratio are also needed Finally, mass to mole conversions

Stoichiometric mole-to-mole conversions 2K(s) + 2H2O  2KOH(aq) + H2(g) Vigorous reaction between potassium and water http://www.youtube.com/watch?v=l9z5-mJ8NZk

Stoichiometric mole-to-mole conversions 2K(s) + 2H2O  2KOH(aq) + H2(g) How can you determine the number of moles of hydrogen produced when 0.0400 mole of pottasium is used? Balanced chemical equation Identify known and unknown Mole to mole conversions

Stoichiometric mole-to-mole conversions 2K(s) + 2H2O  2KOH(aq) + H2(g) KNOWN: 0.0400 mol K UNKNOWN: moles of Both in moles so mole-to-mole conversion MOLE RATIO: Moles of known x moles of unknown = moles of unknown moles of known

Stoichiometric mole-to-mole conversions 2K(s) + 2H2O  2KOH(aq) + H2(g) 0.040 mol K x 1 mol H2 = 0.0200 mol H2 2 mol K If you put 0.040 mol K into water, 0.0200 mol of H2 will be produced.

Example: Stoichiometric Mole-to-Mole Conversion One disadvantage of burning propane (C3H8) is that carbon dioxide (CO2) is one of the products. The released carbon dioxide increases the growing concentration of CO2 in the atmosphere. How many mole of carbon dioxide are produced when 10.0 moles of propane are burned in excess oxygen in a gas grill?

Stoichiometric mole-to-mass conversions You know the number of moles of reactant and produced in a reaction and you want to calculate the mass of another product or reactant. This is an example of mole-to-mass conversion mol known x mol unknown x molar mass unknown = g of unknown mol known mol of known

EXAMPLE: Stoichiometric Mole to Mass Conversion Determine the mass of sodium chloride or table salt (NaCl) produced when 1.25 moles of chlorine gas reacts vigorously with sodium.

Stoichiometric Mass-to-Mass Conversions If you want to carry out a chemical reaction in your laboratory, you need to know how much of each reactant to use in order to produce the mass of product you require.

Example: Stoichiometric Mass-to-Mass Conversion Ammonium nitrate (NH4NO3), an important fertilizer, produce N2O gas and H2O when it decomposes. Determine the mass of water produced from the decomposition of 2.5 g of solid ammonium nitrate.

Steps in Stoichiometric Calculations Write a balanced equation. Determine the moles of the given substance using a mass-to-mass conversion. Determine the moles of the unknown substance from the moles of the given substance

HOMEWORK: Assessment and Practice Problems # 9-19