 CA Standards Std. 3e: Students know how to calculate the masses of reactants and products in a chemical reaction from the mass of one of the reactants.

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CA Standards Std. 3e: Students know how to calculate the masses of reactants and products in a chemical reaction from the mass of one of the reactants or products and the relevant atomic masses.

What is Stoichiometry? The study of quantities of materials consumed and produced in chemical reactions.

How Are Stoich Problems Different?
Includes a balanced equation and molar conversions. Coefficient of equation shows molar relationship (Mole ratio) of reactants and products. Ex: 2H2 + O2  2H2O 2 mol H mol O2  2 mol H2O Ex: Mole Ratio of H2: H2O  2 mol H2 2 mol H2O

Calculating Masses of Reactants and Products
Check if equation is balanced. Convert mass(g) or volume(L) to moles, if necessary. Set up mole ratios. Use mole ratios to calculate moles of desired substituent. Convert moles to mass or volume, if necessary.

Stoich problem Type #1 = 8 mol NH3
Ex 1: How many moles of NH3 can be produced when 4 moles of N2 is reacted with excess H2? N2 + 3H2  2NH3 4 mol N2 2 mol NH3 1 mol N2 = 8 mol NH3

Ex 2: 2N2 + O2  2N2O How many moles of N2 must be reacted with excess O2 to produce 10 moles of N2O? 10 mol N2O 2 mol N2 2 mol N2O = 10 mol N2

Grams of Given to Grams of Unkown Roadmap
MEMORIZE!!! (Mole Ratio) g GIVEN  mol GIVEN  mol UnKnown  g UNKNOWN mol GIVEN

Stoich Problem Type#2 116 g NaCl
Ex 3: 46 grams of Sodium (Na) reacts with an excess Chlorine (Cl). How many grams of Sodium Chloride (NaCl) are formed? 2Na Cl2  2NaCl 46 g Na 1 mol Na 2 mol NaCl 58 g NaCl = 23 g Na 2 mol Na 1 mol NaCl 116 g NaCl

Ex 4: How many grams of water can be prepared from 8 grams of hydrogen at standard conditions?
2 H2 (g) + O2(g) → 2 H2O 8 g H2 1 mol H2 2 mol H2O 18 g H2O 2 g H2 1 mol H2O 2 mol H2 = 72 g H2O

Gas Stoichiometry If reactants and products are at the same conditions of temperature and pressure, then mole ratios of gases are also volume ratios. 3 H2(g) N2(g)  NH3(g) 3 moles H mole N  moles NH3 3 liters H liter N  liters NH3

Gas Stoichiometry 3 H2(g) + N2(g)  2NH3(g)
Ex 5: How many liters of NH3 can be produced when 12 liters of H2 react with an excess of nitrogen? 3 H2(g) + N2(g)  2NH3(g) 12 L H2 2 L NH3 = L NH3 8.0 3 L H2

Ex 6: How many liters of oxygen are required to react completely with 22.4 liters of carbon monoxide, CO, at standard conditions? 2 CO (g) + O2(g) → 2 CO2 (g) 22.4 L CO 1 L O2 = L O2 11.2 2 L CO

END OF UNIT 3: Woo Hoo!

Everyday STOICH S’mores: G2 + C + M  G2CM + + How many S’mores can I make with 5 Graham crackers, 3 marshmallows and 1 Chocolate?

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