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Using Stoichiometry to make predictions about reactions

Using Stoichiometry to make predictions about reactions. Theme: Conservation Predictions % Yield Determining Limiting Reactant. Recipe for ONE apple pie:. 27 apple slices 3 cups flour 2/3 cup of sugar 1 teaspoon cinnamon 2 sticks butter

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Using Stoichiometry to make predictions about reactions

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  1. Using Stoichiometry to make predictions about reactions Theme: Conservation Predictions % Yield Determining Limiting Reactant

  2. Recipe for ONE apple pie: • 27 apple slices • 3 cups flour • 2/3 cup of sugar • 1 teaspoon cinnamon • 2 sticks butter • You have in your pantry: 60 apple slices, 4 cups flour, 5 cup sugar, 2 tablespoons cinnamon, 4 sticks of butter. • How many apple pies can you make?!? • What is your limiting reactant?

  3. Visual Representation of L. R.

  4. Chemistry “Recipes” • Recipe is balanced equation but chemists RARELY make the recipe as is. • What do moles represent? What would be the limiting reactant in the following reaction if you started with 5 moles of aluminum and 12 moles of HCl?

  5. Using the chemical recipe to predict product (without a limiting reactant) • How much O2 gas is generated from the complete decomposition of 5 g of H2O2? • Determine balanced equation. • Determine moles of desired product as controlled by moles of given reactant. • Change moles of desired product to grams.

  6. Practice • Practice predicting outcomes of chemical reactions when given the reactant that controls the reaction.

  7. % Yield • The predicted or theoretical amount of product that can be produced in a chemical reaction is what is calculated by stoichiometry. • The actual yield is what is actually produced in the reaction given uncontrollable sources of error. • % Yield: How much of the theoretical yield did you actually get? • (Actual yield/Theoretical Yield) X 100%

  8. % Yield in a synthesis reaction. • 0.5 g of Mg are reacted with unlimited oxygen according to the following balanced equation: • What is the theoretical yield? • If the actual yield of MgO is 0.73 g. What is the % yield? • Why isn’t it 100%????

  9. Finding the limiting reactant in a chemical “recipe” • A 2.00 g sample of ammonia is mixed with 4.00 g of oxygen.  Which is the limiting reactant and how much excess reactant remains after the reaction has stopped? 4 NH3(g) + 5 O2(g)4 NO(g) + 6 H2O(g)

  10. How to find the limiting reactant • Take each reactant and figure out how many moles of the desired product would be produced. • The reactant that produces FEWER MOLES of product is the limiting reactant and therefore controls the reaction!

  11. Example worked out:

  12. How to find out how much EXCESS there is of the other reactant: • Take the moles of limiting reactant and find out how many moles of product would be needed based on the “recipe”: • Change moles of excess reactant to grams. • Subtract grams needed from grams available to figure out how much would be left over.

  13. Sample Problem worked out

  14. Practice • Limiting reactant problems

  15. Our formal lab: • We will react two aqueous solutions and determine which solution is the limiting reactant. • We will predict how much product we can make (a solid precipitate) based on stoichimetry. • We will use % yield to compare the actual product produced to the expected yield.

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