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Stoichiometry: Understanding Relationships in Chemical Reactions

This presentation by Amadeo Avagadro explores the concept of stoichiometry, including stoichiometric coefficients, molar amounts, and dimensional analysis. Learn how to calculate moles, grams, and atoms in chemical reactions.

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Stoichiometry: Understanding Relationships in Chemical Reactions

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  1. Stoichiometry This presentation has been brought to you by Amadeo Avagadro

  2. Reminder • The numbers in front of the chem. formulas in a reaction are called? • Stoichiometric coefficients • Tell you the amount of the reactant or product in moles • Molar amounts • DIMENSIONAL ANALYSIS

  3. Review • Calculate the number of moles in 35.9 g of Aluminum. • Calculate the amount of grams in 12.03 moles of Si. • How many atoms of Mg are in 2.4 moles?

  4. Avogadro’s Number • Recall that one mole of a substance is equal to 6.022 x1023 units, atoms or molecules. Yo fool, my number be 602-1023 !! Avogadro –chemist, mathematician… ladies man.

  5. Stoichiometry • Stoy-Key-I’m-A-Tree • The mathematics of chemical equations • Calculations involving the amount of reactants and products and their relationships

  6. The coefficient tells you the number of moles The mole ratio is 1:1:2 (1H2:1Cl2:2HCl) You can calculate the molar mass 1 mole of hydrogen reacts with 1 mole of chlorine to produce 2 moles of hydrochloric acid Relationships

  7. 2H2O  2H2 + O2 • What can you tell me about the mole ratio/relationship? • Does this picture make sense? • There is 2x as much H2 produced

  8. Stoichiometric Problems

  9. Stoichiometric coefficients can be used to convert between quantities of reactants and products in a chemical reaction. • 2H2O  2H2 + O2 • For example, the number of moles of H2O produced from 1.57 mol of O2 can be calculated as follows:

  10. Given the following: • 2Al + Fe2O3 Al2O3 + 2Fe • Calc. the amt. of moles of Aluminum needed to create 1.38 mol of aluminum oxide. • 2C2H2 + 5O2  4CO2 + 2H2O • How many moles of oxygen are needed to combust 0.75 moles of C2H2? How many grams is this?

  11. Practice • Zn + 2HCl  ZnCl2 + H2 • Calc. the moles of HCl needed to react with 4 mol g Zn. • How many grams of Zn is this? • 2KClO3  2KCl + 3O2 • How many grams of O2 is produced if 2.50 moles of KClO3 are completely decomposed?

  12. Given the following equation: • Mg(NO3)2 + KOH  Mg(OH)2 + KNO3 • Balance • If we start with 16.0 g of Mg(OH)2, how many moles is this? • How many moles of KOH does this equal? • How many grams of KOH does this equal? • You’ve just correctly done a 3-step problem.

  13. Warm-Up • Given the following equation: • NaN3 Na + N2 • 1. Balance the equation • 2. Classify the equation • 3. Write all molar ratios for the equation (3) • 4. How many grams of NaN3 would be needed to produce 4.5 moles of N2? • 5. How many grams of Na would result if 17.9 g of NaN3 were decomposed?

  14. Up until now we have dealt with mass/mass relationships. • These are not the only relationships in chemistry • Volume/Volume • Is there are relationship (conversion ratio) for relating moles to volume???

  15. YES! • It is called the molar volume • At STP (standard Temp. {25° C} and Pressure {1 atm, 760 mmHg}), 1 mole of any gas takes up a volume of 22.4 L • 22.4 L / 1 mol

  16. Mass/Volume Problem • Sodium bicarbonate is in fire extinguishers, according to the equation: • Na2CO3 Na2O + CO2 • If there is 4.0 g of sodium bicarbonate, what vol. of CO2 gas is produced at STP?

  17. Volume/Volume Problem • How many liters of oxygen is formed from the decomposition of 4.8 liters of water vapor at STP? 2H2O(g) → 2H2(g) + O2(g) • ANSWER: • x L O2 = 4.8 L H2O x 1 mol H2O x 1 mol O2 x 22.4 L O2 22.4 L H2O 2 mol H2O 1 mol O2 = 2.4 L O2

  18. Practice Problem Use the equation below to determine how many liters of oxygen are needed to combust 35 L of C2H2? Remember this would be a complete combustion.

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