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# Stoichiometry 2nd Tri 0910

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### Stoichiometry 2nd Tri 0910

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