Stoichiometry • Stoichiometry---study of the quantitative or measurable relationships that exist in chemical reactions. • From Greek word stoicheion---element • And metron --measure
Stoichiometry (mol-mol) • Mole to Mole: • Write a balanced eq • Identify mol of kn • Identify mol of unkn • Multiply mol of kn time ratio of unkn mol to kn mol from bal eq
Stoichiometry(mol-mol) • If 8.5 mol of Mg burn, how many mol of O2 gas are used? • 2Mg + O2 => 2 MgO • 8.5molMg X 1mol O2/2mol Mg = 4.25 mol O2
Stiochiometry(mol-mol) • If 4 mol of NH4OH react with HCl acid, how many mol of NH4Cl form?
Mol to mass • If 3mol of aluminum react with oxygen, how many grams(mass) of aluminum oxide are formed?
Mass to mol • 20 grams of sulfuric acid react with potassium hydroxide to produce how many moles of water?
Mass to mol • How many moles of bromine liquid form if 120 grams of chlorine react with hydrobromide gas?
Mol to mass • Determine the number of grams of oxygen gas produced if 2.5 moles of potassium chlorate decompose.
Mass-mass---- are calculations used to find the masses of materials involved in reactions • Remember: • in a mass-mass problem the coefficients in the balanced equation represent the relative number of moles
Stoichiometry • Solution process: mass-mass • 1) write a bal eq • 2) determine # of mol of kn substance • 3) determine ratio of unkn substance to kn substance using the balanced eq • 4) convert the mol of unkn to g of unkn
Mass to Mass • Kn(g) x 1mol kn/mm kn x mol ukn/mol kn x mm unk/1 mol kn
Stoichiometry (Mass-mass) • How many g of Ca ( OH)2 will react with 10 g of phosphoric acid? • Solve on the board
Stoichiometry ( mass-mass) • If 100.0 g of Ag react with nitric acid, how many g of H2 gas form?
Mass to Mass problem • If 9.8 g of sulfuric acid react with KOH, how much H2O forms? Name the salt produced.
Mass-Volume Problems • Remember: • Molar volume at STP = 22.4 L • Solution process: • Write a bal eq • Convert g of given to mol • Ratio of relative mol of unkn to kn from bal eq • Volume of 1 mol of gas at STP
Mass-volume problems • Ex: 125 g of sodium azide (NaN3) explodes to produce Na & N2, what volume of N2 gas at STP is produced?
Mass-volume problems • 2NaN3 => 2Na + 3 N2 • 125g/1 X 1mol/65g X 3mol N2/2 mol NaN3 X 22.4 L/1mol = 64.6 L N2
Volume-mass • Find the mass of MgO formed when 44.8 liters of O2 gas reacts with Mg at STP. • 2Mg + O2 => 2 MgO
Volume –volume problems • Ex: What vol of N2 gas is necessary to react with H2 gas to produce 16 L of NH3 gas at STP?
Volume to Volume 3H2 + N2 => 2NH3 16L/1 X 1mol NH3/22.4L X 1mol N2/2mol NH3 X 22.4L N2/1mol N2= 8L
Mass-energy problems • Mass-energy problems involve calculating the heat of reaction from the mass of materials in a reaction
Mass-energy problems may be solved by: • A) write a bal eq • B) convert g of kn to mol • C) multiply the # of kJ of energy over the # of mol of kn from the bal eq
Mass-energy • How much energy is generated by the reaction of 1.99 g of Na2O2 with H2O according to the following equation: • 2Na2O2 + 2H2O => 4NaOH + O2 + 215 kJ • Exothermic or endothermic ? • “q” will be positive or negative ?
When 450 kj of energy is absorbed, Barium hydroxide decomposes to form barium oxide and water. How much energy is absorbed if 36 grams of water forms?
Limiting reactantCh 12Page 364 • Limiting reactant---a reactant that is completely used up in a chemical reaction, limits the extent of the reaction and determines the amount of product made • Excess reactants---reactants that are left over, un-reacted, at the end of the reaction
Limiting reactant • Ex: If 6 g of Ag react with 10 g of O2 to form Ag2O, what is the limiting reactant?
Percentage yield • No reaction can be carried out with perfection. All reactions will yield less than is theoretically possible. The calculated amount of product that should be produced is called expected yield
The ratio of the actual amount of product to the amount of product in a calculated chemical reaction is called percent yield
% yield = actual amount/expected amount X 100 • Reaction A is to make 2.6 L of O2 but the reaction only made 1.9 L. % yield is what? • %yield = 1.9L/2.6L X 100 = 73%
% yield • Ex: when propane reacts with oxygen, carbon dioxide and water are produced. • A) when 7.51 g of propane react with excess oxygen, how many grams of carbon dioxide are formed? • B) If 18.6 g of carbon dioxide is actually formed, what is the % yield?