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Stoichiometric Calculations (Ch. 12 p. 352-367)

Stoichiometry – Ch. 12. Stoichiometric Calculations (Ch. 12 p. 352-367). A. Proportional Relationships. Ratio of eggs to cookies. I have 5 eggs. How many cookies can I make?. 2 1/4 c. flour 1 tsp. baking soda 1 tsp. salt 1 c. butter 3/4 c. sugar. 3/4 c. brown sugar

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Stoichiometric Calculations (Ch. 12 p. 352-367)

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  1. Stoichiometry – Ch. 12 Stoichiometric Calculations(Ch. 12 p. 352-367)

  2. A. Proportional Relationships Ratio of eggs to cookies • I have 5 eggs. How many cookies can I make? 2 1/4 c. flour 1 tsp. baking soda 1 tsp. salt 1 c. butter 3/4 c. sugar 3/4 c. brown sugar 1 tsp vanilla extract 2 eggs 2 c. chocolate chips Makes 5 dozen cookies. 5 eggs 5 doz. 2 eggs = 12.5 dozen cookies

  3. A. Proportional Relationships • Stoichiometry • mass relationships between substances in a chemical reaction • based on the mole ratio • Mole Ratio • is indicated by coefficients in a balanced equation 2 Mg + O2 2 MgO

  4. B. Stoichiometry Steps 1. Write a balanced equation. 2. Write the given/known. 3. Use conversion factors (mole equalities) to cancel units… A. Convert to moles B. use mole ratio (coefficients) to change into new substance, C. then convert to new desired units. 4. Check answer.

  5. Mole ratio - moles  moles • Molar mass - moles  grams • Molarity - moles  liters soln • Molar volume - moles  liters gas • Core step in all stoichiometry problems!!

  6. C. Molar Volume at STP StandardTemperature&Pressure 0°C and 1 atm 1 mol of a gas=22.4 L at STP

  7. C. Other mole equivalents • 1 mole = 22.4 Liters of gas (must be in gas form at STP) • 1 mole = 6.02 x 1023 particles (atoms, mc’s, formula units, ions) • 1 mole = Molar Mass in grams (using the periodic table masses)

  8. C. Molar Volume at STP LITERS OF GAS AT STP Molar Volume (22.4 L/mol) MASS IN GRAMS NUMBER OF PARTICLES MOLES Molar Mass (g/mol) 6.02  1023 particles/mol Molarity (mol/L) LITERS OF SOLUTION

  9. D. Stoichiometric Calculations • Special Case: If converting Liters to Liters, the mole ratio can be used ONLY IF all substances are gas. All other units MUST be changed to moles first. 2H2(g) + O2(g)  2H2O(g) ? L O2needed? 9 Liter produced 9 L H2O 1 L O2 2 L H2O = 4.5 L O2

  10. E. Key things to remember • To be safe, consider there to be two variables, the chemical formula and the units. • Only change one variable within each conversion.

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