Stoichiometry This presentation has been brought to you by Amadeo Avagadro

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

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

Avogadro’s Number Recall that one mole of a substance is equal to x10 23 units, atoms or molecules. Recall that one mole of a substance is equal to x10 23 units, atoms or molecules. Yo fool, my number be !! Avogadro –chemist, mathematician… ladies man.

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

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

What can you tell me about the mole ratio/relationship? What can you tell me about the mole ratio/relationship? Does this picture Does this picture make sense? There is 2x as There is 2x as much H 2 produced 2H 2 O  2H 2 + O 2

Stoichiometric Problems

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

Given the following: Given the following: 2Al + Fe 2 O 3  Al 2 O 3 + 2Fe 2Al + Fe 2 O 3  Al 2 O 3 + 2Fe Calc. the amt. of moles of Aluminum needed to create 1.38 mol of aluminum oxide. Calc. the amt. of moles of Aluminum needed to create 1.38 mol of aluminum oxide. 2C 2 H 2 + 5O 2  4CO 2 + 2H 2 O 2C 2 H 2 + 5O 2  4CO 2 + 2H 2 O How many moles of oxygen are needed to combust 0.75 moles of C 2 H 2 ? How many grams is this? How many moles of oxygen are needed to combust 0.75 moles of C 2 H 2 ? How many grams is this?

Practice Zn + 2HCl  ZnCl 2 + H 2 Zn + 2HCl  ZnCl 2 + H 2 Calc. the moles of HCl needed to react with 4 mol g Zn. Calc. the moles of HCl needed to react with 4 mol g Zn. How many grams of Zn is this? How many grams of Zn is this? 2KClO 3  2KCl + 3O 2 2KClO 3  2KCl + 3O 2 How many grams of O 2 is produced if 2.50 moles of KClO 3 are completely decomposed? How many grams of O 2 is produced if 2.50 moles of KClO 3 are completely decomposed?

Given the following equation: Given the following equation: Mg(NO 3 ) 2 + KOH  Mg(OH) 2 + KNO 3 Mg(NO 3 ) 2 + KOH  Mg(OH) 2 + KNO 3 Balance Balance If we start with 16.0 g of Mg(OH) 2, how many moles is this? 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 moles of KOH does this equal? How many grams of KOH does this equal? How many grams of KOH does this equal? You’ve just correctly done a 3-step problem. You’ve just correctly done a 3-step problem.

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

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

YES! It is called the molar volume 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 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 22.4 L / 1 mol

Mass/Volume Problem Sodium bicarbonate is in fire extinguishers, according to the equation: Sodium bicarbonate is in fire extinguishers, according to the equation: Na 2 CO 3  Na 2 O + CO 2 Na 2 CO 3  Na 2 O + CO 2 If there is 4.0 g of sodium bicarbonate, what vol. of CO 2 gas is produced at STP? If there is 4.0 g of sodium bicarbonate, what vol. of CO 2 gas is produced at STP?

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

Use the equation below to determine how many liters of oxygen are needed to combust 35 L of C 2 H 2 ? Remember this would be a complete combustion. Practice Problem