Create Presentation
Download Presentation

Download Presentation
## Chapter 9/ Stoichiometry

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -

**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?