Stoichiometry Introduction to Chemistry

Stoichiometry Example: 2H 2 + O 2 → 2H 2 O Equivalencies: 2 mol H 2 for every 1 mol O 2 2 mol H 2 for every 2 mol H 2 O 1 mol O 2 for every 2 mol H 2 O

Stoichiometry Example: N 2 + H 2 → NH 3 - Is the equation balanced? - How many moles of hydrogen gas are there in this equation? - How many moles of ammonia? - How many moles of nitrogen gas? 23 3 mol H 2 2 mol NH 3 1 mol N 2

Stoichiometry Stoichiometry ◦ the term used to describe the quantitative relationships of masses or volumes in a chemical reaction Using stoichiometry, we can do the following conversions between two different substances: ◦ moles to molesgrams to grams ◦ grams to molesgrams to volume ◦ moles to gramsvolume to volume

Mole-Mole conversions Steps 1. Make sure equation is balanced 2. Use coefficients to convert from moles of one substance to moles of another substance

Mole-Mole conversions Example:2H 2 + O 2 → 2H 2 O 20 moles of hydrogen gas are combusted to form water. - How many moles of oxygen gas are required? 10 mol O 2

Practice 1) 2H 2 + 1O 2 → 2H 2 O How many moles of water are formed when 20 moles of hydrogen gas are combusted? 20 mol H 2 O

Practice 2)4Fe + 3O 2 → 2Fe 2 O 3 How many moles of oxygen gas are needed to completely react with 85 moles of iron(III)? How many moles of iron oxide are produced? 64 mol O 2 43 mol Fe 2 O 3

Practice 3) 2Al + 3H 2 SO 4 → 3H 2 + Al 2 (SO 4 ) 3 How many moles of aluminum are required to completely react with 25.3 moles of hydrogen sulfate? How many moles of hydrogen gas are produced by this reaction? 16.9 mol Al 25.3 mol H 2

Mass-Mass conversions Steps 1. Make sure equation is balanced 2. Use molar mass and coefficients to convert

Molar Mass Calculations What is the molar mass of H 2 H 2 0 NaCl MgCl 2

Example 2H 2 + 1O 2 → 2H 2 O If 20.0 grams of hydrogen gas are combusted to form water. How many grams of water are formed? How many moles of oxygen gas are required? 180 g H 2 O 5.00 moles O 2

Practice 4) 4Fe + 3O 2 → 2Fe 2 O 3 How many grams of oxygen gas are needed to completely react with 85.0 grams of iron(III)? How many grams of iron oxide are produced? 36.5 g O g Fe 2 O 3

Practice 5) 2Al + 3H 2 SO 4 → 3H 2 + Al 2 (SO 4 ) 3 How many moles of aluminum are required to completely react with 25.3 grams of hydrogen sulfate? mol Al

Practice 5) 2Al + 3H 2 SO 4 → 3H 2 + Al 2 (SO 4 ) 3 How many grams of hydrogen gas are produced when 1.32 moles of aluminum react? 4.0 g H 2

Mass-Mole / Mole-Mass conversions Example: 2H 2 + O 2 → 2H 2 O How many grams of water are produced when 35.2 moles of oxygen gas react? 1270 g water

Mass–Volume Conversions Steps 1. Make sure all chemical formulas are correct and the equation is balanced 2. Use molar mass, coefficients, and molar volume to convert

Mass–Volume Conversions Example: If 125 grams of NaN 3 decompose, how many liters of nitrogen gas are produced? 2NaN 3 → 2Na + 3N L nitrogen gas

Mass–Volume Conversions Example: If 125 grams of NaN 3 decompose, how many liters of nitrogen gas are produced? 2NaN 3 → 2Na + 3N L of CO 2

Volume-Volume Conversions Steps 1. Make sure all chemical formulas are correct and the equation is balanced 2. Use coefficients to convert

Volume-Volume Conversions Example: If 15.5 liters of N 2 react with hydrogen gas, how many liters hydrogen gas are needed to react completely? 3H 2 + N 2 → 2NH L H 2

Volume-Volume Conversions Example: If 0.38 liters of H 2 react with chlorine gas, how many liters of hydrochloric acid are produced? H 2 + Cl 2 → 2HCl 0.76 L HCl

Limiting Reactant Limiting reactant (a.k.a. limiting reagent) ◦ the reactant that is completely consumed during the reaction Finding the limiting reactant: 1.Make sure all chemical formulas are correct and the equation is balanced 2.Use stoichiometry to calculate the amount of product that is produced for both reactants. 3.The reactant that produces the least amount of product is the limiting reagent

Limiting Reactant Example: 2H 2 + O 2 → 2H 2 O 12.0 moles of hydrogen gas reacts with 12.0 moles of oxygen gas. Which is the limiting reagent? How many moles of water are made during this reaction? H 2 is limiting reagent 12.0 mol water

Limiting Reactant Example:2Mg + O 2 → 2MgO 3.51 moles of magnesium reacts with 4.98 moles of oxygen gas. Which is the limiting reagent? How many moles of product are made? Mg is limiting reagent 3.51 mol MgO

Limiting Reactant Example: 2H 2 + O 2 → 2H 2 O 12.0 grams of hydrogen gas reacts with 12.0 grams of oxygen gas. Which is the limiting reagent? How many grams of water are made during this reaction? O 2 is limiting 13.5 g H 2 O

Limiting Reactant Example:2Mg + O 2 → 2MgO 30.0 grams of magnesium reacts with 35.0 grams of oxygen gas. Which is the limiting reagent? How many moles of product are made? Mg limiting 1.23 moles MgO

Percent Yield Percent Yield = actual yield x 100 expected yield % yield describes the percent of the expected yield that was actually obtained

Percent Yield Example: Cu + 2AgNO 3 → 2Ag + Cu(NO 3 ) g of copper are placed in a solution of silver (I) nitrate containing excess AgNO g of silver (Ag) are actually produced during this reaction. What is the percent yield for silver (Ag) for this reaction? 89.4% yield

Percent Yield Example: Al(NO 3 ) 3 + 3NaOH → Al(OH) 3 + 3NaNO g of Al(NO 3 ) 3 are placed in a solution of NaOH containing excess NaOH g of Al(OH) 3 are actually produced during this reaction. What is the percent yield for Al(OH) 3 for this reaction? 93.8% yield

Law of Conservation of Mass You can use the law of conservation of mass to solve for an unknown amount of substance Steps: 1. Find the balanced equation 2. Label grams of each substance 3. Drop down “+” signs and turn the arrow into an equals sign 4. Solve for the unknown mass

Law of Conservation of Mass Example: If 4.30 grams of sodium react completely with 1.92 grams of chlorine, how many grams of NaCl will be produced? 2Na + Cl 2 → 2NaCl 6.22 g NaCl

Law of Conservation of Mass Example: Fe reacts completely with MgCl 2. Find the mass of Mg produced. Fe + MgCl 2 → Mg + FeCl 3 Trial Mass of Fe (g) Mass of MgCl 2 (g) Mass of Mg (g) Mass of FeCl 3 (g) x g Mg

SOL covered during lesson CH 3 a, b, c CH 4 b