1 / 0

Reaction Stoichiometry problems: how chemists cook

Reaction Stoichiometry problems: how chemists cook. Review of Cooking and stoichiometry. THE RECIPE. 3. 1. +. 2. +. 300 g/block. 200 g/box. 500 g/dozen. 1900 g/ souffle. How many….to make whole # of souffles ? . 12. How many boxes of cream to make 4 souffles ?. 2.

dot
Download Presentation

Reaction Stoichiometry problems: how chemists cook

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Reaction Stoichiometry problems:how chemists cook
  2. Review of Cooking and stoichiometry THE RECIPE 3 1 + 2 + 300 g/block 200 g/box 500 g/dozen 1900 g/souffle How many….to make whole # of souffles ? 12 How many boxes of cream to make 4 souffles ? 2 600 grams cheese makes how many souffles ? How many grams of eggs combine with 9 boxes of cream ? 3000 g 2 48 eggs combine with how many blocks of cheese ?
  3. Reaction Stoichiometry problems:how chemists cook Sample of Typical Reaction stoichiometry problems C3H8+ 5O2 3CO2+ 4H2O BALANCED Example 1: (reactant  product) Given 16 grams of O2 predict the how many molecules of CO2 that can form.
  4. Another example of Reaction Stoichiometry problems:how chemists cook Typical Reaction stoichiometry problems (cont.) C3H8+ 5O2 3CO2+ 4H2O Example 2: (limiting reactant product) Given 1 gram of O2 and 1 gram of C3H8, what is the maximum weight of H2O we can make ?
  5. “What does reactionstoichiometry have to do with anything really important and practical ?”
  6. Individual fuel injectors Stoichiometric control in the real world Gas/O2 ratio and flow rate to each fuel injector changes constantly The GAME CHANGER: Microchips controlling injector mix stoichiometry V-8 fuel injection module Goes under here*
  7. Variation of mpg and hp vs time for light-duty trucks 1975 US Congressional mandate for 23.5 mpg fleet average enacted 8 bit PROM chips become reasonably cheap
  8. Reaction Stoichiometry and the story of Goldilocks and the 3 Bears…a demo Mama Bear O2/C3H8>>5 Papa Bear O2/C3H8<<5 Baby Bear O2/C3H85 Goldilocks: wantonly commits breaking and entering felony The outraged victims….
  9. Simple mol-mol stoichiometry conversions C3H8 + 5O2-------- 3CO2 + 4H2O How many moles of O2 will burn to form 1.2 moles of CO2 ? Method 1: factor label way 1) given 2) want *5 mol O2 3 mol CO2 1.2 mol CO2 = ? mol O2 2 3) Use reaction stoichiometry coefficients in right ratio to cancel and connect…which ratio ???
  10. Mol-mol stoichiometry conversions (continued) Method 2: `mole ratios’ way C3H8+ 5O2-------- 3CO2 + 4H2O 1.2 mol ?? m Problem stated visually How many moles of O2will burn to form 1.2 moles of CO2 ? 1) ratio `wanted’ moles in numerator to given in denominator m 1.2 5 3 2) Set equal to matching coefficients for compounds given in reaction…which ??? = 1.2*m= 1.2 *5 1.2 3 = 2 3)Solve for m
  11. More complex stoichiometry problem done 2 ways MW 44 32 44 18 g/mol C3H8+ 5O2 3CO2+ 4H2O 22 grams of C3H8burned with O2 makes howmany grams of H2O ? Method 1: factor label 22 g C3H8 x 1 mole C3H8 44 g C3H8 4 mol H2O 1 mole C3H8 x 18 g H2O 1 mol H2O x 1) Given = ?? g H2O 36 2) Want 3)Find ratios that lead to desired units from reaction and MW …which ???...do on board
  12. Method 2:mole ratio way (Board first) 22 grams of C3H8burned with O2 makes howmany grams of H2O ? 44 32 44 18 g/mol Given: Problem stated visually C3H8+ 5O2 3CO2+ 4H2O ?? g 22 g 0) convert all given masses and molecule counts to moles 1) ratio `wanted’ moles in numerator to given in denominator 2) Set equal to matching coefficients for compounds given in reaction…which ??? 3) Solve for wanted moles 4) Convert wanted moles to wanted final units (grams)
  13. Method 2:mole ratio way 22 grams of C3H8burned with O2 makes howmany grams of H2O ? 44 32 44 18 g/mol Given: Problem stated visually C3H8+ 5O2 3CO2+ 4H2O ?? g 22 g 0) convert all given and molecule counts to moles 22 g C3H8* 1 mol C3H8 44 g C3H8 = 0.5 mol C3H8 1) ratio `wanted’ moles in numerator to given in denominator m =mol H2O 0.5 mol C3H8 = 4 1 2) Set equal to matching coefficients for compounds given in reaction…which ???
  14. Method 2:mole ratio way 22 grams of C3H8burned with O2 makes howmany grams of H2O ? 44 32 44 18 g/mol Given: C3H8+ 5O2 3CO2+ 4H2O ?? g 22 g 3) Solve for wanted moles m 0.5 = 4 1 0.5 * *0.5 = 2 mol H2O 4) Convert wanted moles to wanted final units (grams) 2 mol H2O * 18 g H2O 1 mole H2O = 36 g H2O
  15. AN ANECDOTE An `out-of-towner’ visiting NYC for the first time asks Joshua Bell (world’s greatest violinist): “How do you get to the Lincoln Center for the Performing Arts ?” Joshua’s answer (supposedly): “Practice, practice, practice….”
  16. Exercise 4: Sample Reaction 1 Chemical Stoichiometry Problems Solved in Detail Sample reaction 1 C3H8 + 5O2------ 3CO2 + 4H2O (BOOM) 44 32 44 18 g/mol First U try them…then I’ll work through sample reaction 1: problems a-f the mole ratio way
  17. C3H8 + 5O2--------3CO2 + 4H2O (BOOM) 44 32 44 18 g/mol a) moles to moles How many moles of O2will burn to form 0.60 moles of CO2 ? 1) Set up mole ratio Mol O2 =m(O2) = 5 Mol CO2 0.6 3 2) Solve for m m(O2) = 5*0.6 => m=1 3
  18. C3H8 + 5O2--------3CO2 + 4H2O (BOOM) 44 32 44 18 g/mol b) moles to weight How many grams of CO2are generated if 0.00757 moles of C3H8 are burned? Set up mole ratio Mol CO2= m(CO2)_ = 3 Mol C3H8 0.00757 1 2) Solve for m =0.02217 m(CO2) = 3*0.00757 3) Convert moles m to weight Weight CO2= m(CO2) * MW(CO2) = 0.02217*44= 1 g
  19. C3H8 + 5O2--------3CO2 + 4H2O (BOOM) 44 32 44 18 g/mol c) weight to moles How many moles of H2O form if 11 g of C3H8 are burned ? 1) convert non-moles to moles 11 g C3H8* 1 mol C3H8 44 g C3H8 = 0.25 mol C3H8 2) set up mole ratios mol H2O = 4 = m(H2O) mol C3H8 1 0.25 Solve for m 4*0.25 = m(H2O) =1 mol H2O 5
  20. C3H8 + 5O2--------3CO2 + 4H2O (BOOM) 44 32 44 18 g/mol d) weight to weight How many grams of O2are needed to burn 0.275 g C3H8 ? 0.275/44=0.00625 mol C3H8 1) Convert gmole 2a)Ratio target mol/known mol Mol O2/mol C3H8=5/1 = m(O2)/0.00625 2b) solve for target moles, m m(O2) = 5*0.00625 = 0.03125 3) Convert target moles to mass desired Weight O2 = m(O2)*MW(g/mol) =0.03125*32 = 1 g O2
  21. C3H8 + 5O2--------3CO2 + 4H2O (BOOM) 44 32 44 18 g/mol e) weight to count How many molecules of CO2form if 0.398 g H2O results ? 0.398 g H2O *1 mol H2O = 0.02211 mol H2O 18 g H2O m(CO2) = 3 = m(CO2) m(H2O) 4 0.02211 m(CO2)= 0.0165 m(CO2)= 3*0.02211 4 =1*1022 Molecule count = m(CO2) *6.02*1023
  22. C3H8 + 5O2--------3CO2 + 4H2O (BOOM) 44 32 44 18 g/mol f) count to weight How many grams of O2are needed to form 1.50*1022 molecules of H2O ? 1.5*1022 6.02*1023 Mole H2O = =0.02491 mol H2O Mol O2 Mol H2O = 5 = m(O2) 4 0.02491 m(O2)= 5*0.02491 4 =0.03114 Weight O2= m(O2)*MW (g/mol) = 1 g O2 =0.03114*32
  23. Sample Reaction 2 6HCl + 2Al ----- 2AlCl3 + 3H2 36 27 123 2 g/mol moles to moles: How many moles of Al must be added to produce 15 moles of H2 ? 10 mol Al b)moles to weight: How many grams of H2are created by reacting 10 moles of HCl ? 10 grams H2
  24. Sample Reaction 2 (home practice) 6HCl + 2Al ----- 2AlCl3 + 3H2 36 27 123 2 g/mol c) weight to moles: How many moles of HClcan combine with 90 g of Al ? 10 moles HCl d) weight to weight: How many grams of Al must react to form 1.1111 grams of H2 ? 10 grams Al
More Related