Stoichiometry

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PowerPoint introducing Stoichiometry with examples.

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Stoichiometry

  1. 1. Stoichiometry <ul><li>Using a balanced chemical equation to determine how much reactant or product is consumed or produced in a chemical reaction. </li></ul><ul><li>2 H 2 (g) + O 2 (g)  2 H 2 O (l) </li></ul><ul><ul><li>How many moles of H 2 O are produced from the reaction of 2 moles of H 2 ? </li></ul></ul><ul><ul><li>How many moles of O 2 are required to produce 4 moles of H 2 O? </li></ul></ul>Chemical equation = recipe
  2. 2. Chemical Equations <ul><li>2 H 2 (g) + O 2 (g)  H 2 O (l) </li></ul>http://www.chemistry.ohio-state.edu/betha/nealChemBal/ 4 moles molecules + 2 moles molecules  4 moles molecules Coefficients in Chemical Equation represents mole ratios
  3. 3. Stoichiometry “Chemical Equation = recipe” <ul><li>2 bread slices + 1 cheese slice  1 sandwich </li></ul><ul><ul><li>Suppose need to make as many cheese sandwiches as possible for a party and have 20 slices of bread...how many slices of cheese are needed? </li></ul></ul><ul><li>By inspection of recipe ( chemical equation ) </li></ul><ul><li>Or use coefficient ratio ( mole ratio ) from equation: </li></ul><ul><ul><li>2 bread slices = 1 cheese slice </li></ul></ul><ul><li>cheese slices = 20 bread slices x </li></ul><ul><li>= 10 cheese slices needed </li></ul>Image source: http://www.fotosearch.com/clip-art/sandwich.html
  4. 4. <ul><li>want = given x conversion factor </li></ul><ul><ul><li>Conversion factor in mole-mole stoichiometry problems is the mole ratio or coefficient ratio. </li></ul></ul>Stoichiometry
  5. 5. Stoichiometry <ul><li>4 Fe + 3 O 2  2 Fe 2 O 3 </li></ul><ul><li>How many moles of Fe 2 O 3 will be produced from the reaction of 1.50 mol of iron? </li></ul><ul><li>… .mol Fe 2 O 3 = 1.50 mol Fe x = 0.75 mol Fe 2 O 3 </li></ul>Mole ratio is coefficient ratio
  6. 6. Stoichiometry – using grams <ul><li>Suppose the given is grams, not moles… </li></ul><ul><li>Consider the un balanced reaction: </li></ul><ul><li>Al (s) + Fe 2 O 3 (s)  Al 2 O 3 (s) + Fe (l) </li></ul><ul><li>If you react 4.0 g of Al with excess Fe 2 O 3 , how many moles of Fe will be produced?? </li></ul><ul><li>First balance the equation: </li></ul><ul><li>2 Al (s) + Fe 2 O 3 (s)  Al 2 O 3 (s) + 2 Fe (l) </li></ul><ul><li>Chemical equation speaks to us in moles, not grams! So to use the mole ratio it gives us (2mol Al: 2 mol Fe), </li></ul><ul><ul><li>first need to convert 4.0 g Al to moles of Al </li></ul></ul><ul><ul><li>Then take moles of Al and “convert” to moles of Fe using mole ratio from balanced equation (coefficient ratio) as was done on previous slides. </li></ul></ul>
  7. 7. <ul><li>Road map: </li></ul>Stoichiometry – using grams
  8. 8. Stoichiometry – using grams <ul><li>Suppose we wanted to solve for grams, not moles </li></ul><ul><li>2 Al (s) + Fe 2 O 3 (s)  Al 2 O 3 (s) + 2 Fe (l) </li></ul><ul><li>Question: If you react 4.0 g of Al with excess Fe 2 O 3 , how many grams of Fe will be produced? </li></ul><ul><li>Road map is same as before, except one last step to convert mol Fe to g Fe. </li></ul><ul><ul><li>Remember that to do any stoichiometry problem, you must be in the language of moles since the chemical equation (source of relationship or conversion factor) only speaks to us in moles , not grams! </li></ul></ul>
  9. 9. <ul><li>Road map: g -> mol -> mol -> g </li></ul>Stoichiometry – using grams

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