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Transcript
Chapter 9 Chemical Quantities Chapter Objectives: To understand the molecular and mass information given in a balanced equation. To learn to use a balanced equations to determine relationships between moles of reactants and moles of products. To learn to relate masses of reactants and products in a chemical reaction. To carry out mass calculations that involve scientific notation. To understand the concept of limiting reactants. To learn to recognize the limiting reactant in the reaction. To learn to use the limiting reactant to do stoichiometric calculations. Information Given by Chemical Equations Chemical change involves: 1. _____________________________ of atom groupings. 2. one or more substances changing to ______________________________ The equation for a chemical reaction gives you the relative numbers of ___________________ and _______________ molecules. Gaseous carbon monoxide and hydrogen react to produce liquid methanol (CH 3OH) Write an unbalance chemical equation for this reaction: ________________________ + ______________________ →_________________________ + ______________________ →_________________________ Now, balance the equation ________________________ Write three ways the information given in the balanced chemical equation can be interpreted: ________________________ + ______________________ → _________________________ ________________________ + ______________________ → _________________________ ________________________ + ______________________ → _________________________ Gaseous propane (C3 H8 ) reacts with oxygen gas to produce carbon dioxide and water Write a balanced chemical equation: → Write down the same reaction in terms of molecules. → Write down the same reaction in terms of moles. → Mole-Mole relationships A sandwich requires 2 slices of bread and 3 slices of meat. Write an equation to represent this. ____B + ____M _____B2M3 10 B + 15 M __?_ B2M3 Write an equation to represent __________________+ _________________ _________________ __________________+ _________________ _________________ The ratio of moles of one substance to moles of another substance in a balanced chemical equation is called the __________________________________. How many moles of water can be produced with 2.9 moles of oxygen gas? O2 (g) 2H 2 (g) 2H 2 O(l) How many moles of oxygen gas are there compared to moles of water in the balanced equation? 2.9 mol O2 x ___________ _____ mol H 2 O How many moles of methanol can be produced with 5.67 moles of hydrogen gas? CO(g) 2H 2 (g) CH 3OH(l) 5.67 mole H2 x (----------------------------) = _____mole CH OH Homework: Chapter 9 Assessment (p. 310, #2,3,6,8,9,10) 3 Mass Calculations C3H8(g) + O2(g) CO2(g) + H2O(g) What mass of oxygen will be required to react with exactly 44.1 g or propane? What do we know? -- C3H8(g) + O2(g) CO2(g) + H2O(g) -- 44.1 g of propane How do we solve this problem? Balance the equation: ____C3H8(g) + ____O2(g) ____CO2(g) + ____H2O(g) What next? 1. Convert grams of propane to moles of propane ( 44.1 g C3H8(g) X -------------------------------------------- ) = __________mole C3H8(g) 2. Determine the number of moles of oxygen using the coefficients in the balanced chemical equation: __________ mole C3H8(g) reacts with ____________ O2(g) ( __________mole C3H8(g) X ------------------------------------------ ) = ____________mole O 3. Use the molar mass of oxygen to calculate the grams of oxygen needed: ( _________ mole O2(g) X ------------------------------------------ ) = ____________g O 2(g) 2(g) Steps to Calculate the Mass of Reactants and Products in a Chemical Reaction Step 1________________________________________________________________________________ Step 2________________________________________________________________________________ Step 3________________________________________________________________________________ Step 4________________________________________________________________________________ Step 5________________________________________________________________________________ What is Stoichiometry? Stoichiometry - _________________________________________________________________________ __________________________________________________________________________ Practice: HF(aq) + SiO2(s) SiF4(g) + H2O(l) A. Calculate the mass of hydrogen fluoride needed to react with 5.68 g of silica (SiO2). B. Calculate the mass of water vapor produced in the reaction. List the steps required for solving A. 1. ____________________________________ 2. Convert the mass of silica to _____________________. 3. Use balanced equation to set up the mole ratio between __________________ and ____________________. 4. Use mole ratio to calculate number of moles of _______________________. 5. Convert from ________________ HF to ___________________ HF. Solve part B below. Show all work. Homework: Chapter 9 Assessment (p. 310, #11,13a-d,14a-d,15a-b,16a-b,17,18,21,24) Limiting Reactants and Percent Yield Making a sandwich requires 2 pieces of bread, 3 slices of meat and one slice of cheese. Write a chemical equation to represent making one sandwich: ___B + ___M + ___C ____S How many sandwiches could you make if you had: 20 slices of bread 24 slices of meat 12 slices of cheese Determine how many sandwiches can be made with each of the following ingredients: 20 slices of bread x 24 slices of meat x 1 sandwich ______ sandwiches 2 slices of bread 1 sandwich ______ sandwiches 3 slices of meat 12 slices of cheese x 1 sandwich ______ sandwiches 1 slice of cheese How many sandwiches can be made? _________ What will be left over? ___slices of bread ___slices of meat ___slices of cheese The ratio of N2 to H2 necessary to produce NH3 is ______N2 and ____H2 which results in the production of _______NH3. Draw in the NH3 molecules that will result from the reaction of hydrogen and nitrogen in the above container. How many NH3 molecules will be formed? _______________________ What will be left over?__________________________ To determine how much product will be formed from a given mixture of reactants, we have to look for the reactant that is ____________________________ -- the one that runs out __________________ and thus limits the amount of product that can form. The reactant that runs out first and thus limits the amount of products that can form is called the _________________________________________________________. Sample problems: CH4(g) + H2O(g) H2(g) + CO(g) What mass of water is required to react exactly with 249 g of methane? What do we know? 1. balanced chemical equation: 2. ______g CH4(g) How do we solve this? Mass of CH4(g) moles of CH4(g) moles of H2O (g) mass of H2O (g) Step 1. Balance the equation: ____CH4(g) + ____H2O(g) ____H2(g) + ____CO(g) Step 2. Convert mass of methane to moles of methane: 249 g CH 4 x ______mol CH 4 ______ g CH 4 _______g CH 4 Step 3. Using balanced equation determine the ratio between water and methane: ______mol CH 4 x ______mol H 2 O ______ mol H 2 O _______mol CH 4 Step 4. Determine the mass of oxygen required by converting moles of oxygen to grams. ______mol H 2 O x ______g H 2 O ______ g H 2 O _______mol H 2 O Practice Problem: Lithium nitride, an ionic compound containing Li+ and N3- ions, is prepared by the reaction of lithium metal and nitrogen gas. Calculate the mass of lithium nitride formed from 56.0 g of nitrogen gas and 56.0 g of lithium metal in the unbalanced reaction: Li(s) + N2(g) Li3N(s) Step 1. Balance the chemical equation _____Li(s) + _____N2(g) _____Li3N(s) Step 2. Convert known masses of reactants to moles. 56.0 g Li x ______mol Li ______ g Li _______g Li 56.0 g N 2 x ______mol N 2 ______ g N 2 _______g N 2 Step 3. Using the numbers of moles of reactants and the appropriate mole ratios, determine which reactant is limiting. ______mol Li mol Li x ______ moles of N 2 required _______mol N 2 Which is greater moles of N2 available (step 2) or moles of N2 required (step 3)? What is the limiting reactant? ______________________ Step 4. Using the amount of the limiting reactant and the appropriate mole ratios, compute the number of moles of the desired product. ______ mol Li x ______mol N 2 ______ mol N 2 _______mol Li Step 5. Convert from moles of product to grams of product using the molar mass. mol N 2 x ______mol N 2 ______ g N 2 _______g N 2 Homework: Chapter 9 Assessment (p. 310, #30, 31, 35, 37, 38) Percent Yield _______________________________ the maximum amount of a given product that can be formed when the limiting reactant is completely consumed. ________________________________the actual yield of a product as the percentage of the theoretical yield. How do you calculate Percent Yield? Homework: Chapter 9 Assessment (p. 310, #40, 42, 44, 45)