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# Stoichiometry 2nd Tri 0910

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• All calculations about how much of a chemical to use for a reaction are based on stoichiometry. Chemists who developed airbags in cars had to determine exactly how much of a chemical to use so that the bag would inflate quickly enough. They also had to design it to produce the exact right amount of gas so that the bag would not over- or underinflate.
• Don&apos;t forget to balance the equation!
• ### Transcript

• 1. Shhhh… Don’t say the “S” word! (But what is the “S” word in Chemistry?)
• 2. Stoichiometry ! Stoichi-what??!!
• 3. Stoichiometry !
• 4. To Review...
• 5.
• Method:
• Practice:
Find the mass on the PT for each element, multiply by subscripts; add them together. What is the molar mass of Ba(C 2 H 3 O 2 ) 2 ? 255.3 g/mol
• Calculating Molar Mass (section title)
• 6. [What is the molar mass of Ca(OH) 2 ?]
• [57.1 g/mol]
• [74.1 g/mol]
• [114.2 g/mol]
• [none of these]
• 7. Changing Grams to Moles
• Method:
• Practice:
• Use molar mass and dimensional analysis to convert
How many moles are contained in 23.995 g of barium acetate? (see notes above) 0.09399 mol
• 8. In order to change grams to moles, you must divide the molar mass by the mass.
• True
• False
• 9. [Convert 15.0 g of CO 2 to moles. ]
• 0.341 mol
• 59 mol
• 660. mol
• 10. Changing moles to grams
• Method:
• Practice:
• Use molar mass and dimensional analysis to convert
How many grams are in .000115 moles of barium acetate? 0.0294 g
• 11. You convert moles to grams by multiplying moles by molar mass.
• True
• False
• 12. What is the mass of 3.4 moles of aluminum hydroxide, Al(OH) 3 ?
• 156.4 g
• 207.4 g
• 265.2 g
• 294.1 g
• 13. Balancing equations
• Method:
• Practice:
• Count atoms of each element on each side of the equation.
• Add coefficients (big numbers in front) to make each kind of atom the same on both sides.
C 5 H 12 + O 2 --> CO 2 + H 2 O C 5 H 12 + 8 O 2 --> 5 CO 2 + 6 H 2 O
• 14. more balancing practice...
• PbO 2  PbO + O 2
• AlCl 3 + Na 2 CO 3  NaCl + Al 2 (CO 3 ) 3
• 2 PbO 2  2 PbO + O 2
• 2 AlCl 3 + 3 Na 2 CO 3  6 NaCl + Al 2 (CO 3 ) 3
• 15.
• 1
• 2
• 3
• 4
Given the unbalanced equation: Mg(ClO 3 ) 2 -> MgCl 2 + O 2 What is the coefficient of O 2 when the equation is balanced correctly using the smallest whole number coefficients?
• 16. Stoichiometry is...
• the calculation of quantities in chemical equations
• important because it allows chemists to determine how much of a reactant is needed or how much product can be made
• based on balanced chemical equations
• 17. General Steps (section title)
• Convert given amount to moles.
• Put calculated moles over 'X' and set it equal to the ratio.
• Set up a ratio of the coefficients of the given over the unknown.
• Solve for 'X' (cross-multiply & divide)
• Convert moles to the unit requested.
• 18. Mole Ratios
• Used to determine the proportions that chemicals react with each other
• Determined by looking at the coefficients in the balanced equation
• Ex. 2H 2 + O 2  2H 2 O
• Ratio of H 2 to O 2 is 2:1
• Ratio of H 2 O to H 2 is 2:2
• 19.
• 1:1
• 1:2
• 3:1
• 3:2
In the reaction, N 2 + 3 H 2 --> 2 NH 3 , what is the mole ratio of hydrogen to nitrogen?
• 20. Mole-Mole problems (section title)
• Recognizing: Given is in moles; unknown is in moles
• Practice: C 3 H 8 + O 2  CO 2 + H 2 O How many moles of CO 2 can be produced by .675 moles of C 3 H 8 ?
2.03 mol CO 2 3 5 4
• 21. Given the reaction CH 4 + 20 2 --> C0 2 + 2H 2 0, What amount of oxygen is needed to completely react with 1 mole of CH 4 ?
• 2 moles
• 2 atoms
• 2 grams
• 2 molecules
• 22. Given the reaction: C 6 H 12 O 6 + 6O 2 -> 6CO 2 + 6H 2 O How many moles of C 6 H 12 O 6 are needed to produce 24 moles of carbon dioxide?
• 1.0 mol
• 12 moles
• 24 moles
• 4.0 moles
• 23. Mass-Mass problems (section title)
• Recognizing: given is in grams, unknown is in grams
• Practice – C 3 H 8 + O 2  CO 2 + H 2 O What mass of propane is needed to produce 44.5 grams of water?
27.2 g C 3 H 8 Any time you calculate an amount of product from a balanced equation, this is called “ Theoretical Yield ” 3 5 4
• 24. Volume-Volume problems: (section title)
• 1 mole of any gas at STP (standard temperature and pressure) = 22.4 L
• Recognizing – both given and unknown are in liters or mL
• Practice – C 3 H 8 + O 2  CO 2 + H 2 O What volume of oxygen gas is needed to produce 50.0 L of water vapor?
62.5 L O 2 *** Refers to volume of gases 5 3 4
• 25. How do I get to Walmart??
• 26. Mass & Volume Problems (section title)
• Recognizing: given is either in grams or liters; unknown is also in either one
• Practice:
C 3 H 8 + O 2  CO 2 + H 2 O What volume of CO 2 gas can be produced when 150.0 g of propane are burned? 229.1 L CO 2 Any time you calculate an amount of product from a balanced equation, this is called “ Theoretical Yield ” 5 3 4
• 27. Limiting Reactant
• The chemical in a reaction that will be used up first is the limiting reactant ; controls how much product can be made
• The reactant in excess is the one(s) not used up first
• 28.
• A is the limiting reactant
• B is the limiting reactant
• There is no limiting reactant
• Both A and B are limiting reactants
In the reaction A + B --> C + D , if element B is in excess, then -
• 29. To determine limiting reactant…
• For each reactant, do a stoic problem to determine how many moles of a product can be made. (If there is more than one product, just pick one.)
• Which ever reactant leads to the least amount of product is the limiting reactant.
• 30. Limiting Reactant Practice:
• Practice: C 3 H 8 + O 2  CO 2 + H 2 O
• If you begin with 45.0 g of propane and 65.0 g of oxygen, what is the limiting reactant?
O 2 is the limiting reactant 5 3 4
• 31. In the given equation, which substance is limiting, if 3.7 moles of potassium, K are reacted with 3.7 moles of nickel sulfate, Ni 2 SO 4 ?
• K
• K 2 SO 4
• Ni
• NiSO 4
2K + NiSO 4  K 2 SO 4 + Ni
• 32. More Stoic stuff…
• Actual yield is how much product was made.