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Stoichiometry

Stoichiometry. Ch 12. Ch 12 Objective. 4170.29 use fundamental chemical relationships; Chemical reactions are written as chemical equations, which demonstrate the Law of Conservation of Mass through stoichiometric relationships. Stoichiometry uses Law of Conservation of Matter.

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Stoichiometry

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  1. Stoichiometry Ch 12

  2. Ch 12 Objective • 4170.29 use fundamental chemical relationships; Chemical reactions are written as chemical equations, which demonstrate the Law of Conservation of Mass through stoichiometric relationships.

  3. Stoichiometry uses Law of Conservation of Matter • Remember that “what goes in, has to come out” in a chemical reaction • Matter (mass) changes, it is not created or destroyed. • We can use this fact to determine unknown amounts in a reaction.

  4. Stoichiometry • Deals with the amount of substances involved in chemical reactions. • Stoichiometry is similar to using a recipe for cooking in that it’s based on ratios. • After all, cooking is a chemical reaction.

  5. Example recipe for chocolate chip cookies • 2 cups butter24 oz. chocolate chips4 cups salt2 cups brown sugar2 tsp. soda1 teaspoon flour2 cups sugar4 eggs2 tsp. baking powder2 tsp. vanilla • Stoich, like cooking, is based on ratios

  6. Mole Ratio • Mole ratio is a ratio between the number of moles (coefficients) of any 2 substances in a balanced chemical equation. N2(g) + 3H2(g)  2NH3(g)

  7. Mole-mole, Mole-mass & Mass-mass relationships • We can use grams or moles of the given part of a reaction to solve for grams or moles of the unknown part of a reaction. • We can also use particles* (atoms, molecules, formula units, electrons, etc.) in stoichiometry problems. *Remember to use 6.02 x 1023 for these types!

  8. Steps: 1. Write & balance the equation.(if needed) Use Dimensional Analysis to: 2. Convert the given substance into moles (if it’s in a different unit than moles) 3. Use the coefficients as the mole ratiobetween the given substance and the substance you are asked to solve. 4. Convert moles into the required unit.

  9. Limiting reagent • Also called limiting reactant • The substance that controls the quantity of product that can be formed in a chemical reaction. • Simply put, the reactant that runs out first “limits” how much product is made. • The other reactant is said to be in excess because there is more than enough.

  10. Percent Yield • This compares the actual amount of product from a reaction with the amount calculated from stoichiometry. • In other words, you are comparing how much was actually produced in the experiment to how much should have been produced. actual yield % yield = --------------------- X 100 theoretical yield

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