Honors Chemistry Ch. 9 Stoichiometry

Mole? 6.02 x of whatever is being counted 1 mole of pencils = ? 6.02 x pencils ½ mole of markers? 3.01 x markers

Percent Composition? the % of mass an element contributes to the total compound mass. = 100 element mass compound mass

Remember: If you want full credit, SHOW YOUR WORK and units!!!

2H 2 + O 2  2H 2 O Ratio of H to O? 2:1 What if you end up with 6 H 2 O molecules?

Stoichiometry: study of quantitative relationships between reactants and products Used to determine unknown quantities

C 3 H 8 +5O 2 → 3CO 2 +4H 2 O Molar mass C 3 H 8 ? 44 g … of oxygen? 32 g For every mole propane, how much O 2 ? 5 mol For a dozen molecules C 3 H 8, how much O 2 ? 5 dozen

C 3 H 8 +5O 2 → 3CO 2 +4H 2 O How much O 2 reacts with 1 g C 3 H 8 ? 1 g C 3 H 8 l mol C 3 H 8 5 mol O 2 44 g C 3 H 8 1 mol C 3 H 8 = mol O 2

C 3 H 8 +5O 2 → 3CO 2 +4H 2 O Conservation of mass Reactants: 3(12 amu) + 8(1 amu)+10(16 amu) =204 amu Products: 3(12amu) +6(16 amu)+8(1 amu) + 4(16 amu) = 204 amu

C 3 H 8 +5O 2 → 3CO 2 +4H 2 O How many moles water form from 3.2 mol C 3 H 8 ? 3.2 mol C 3 H 8 4 mol H 2 O 1 mol C 3 H 8 = 12.8 mol H 2 O

Key to Stoichiometry: Molar Ratios!!! = molar coefficients unknown molar coefficients known Comes from balanced chemical equation

Mole-mole conversions: To determine the quantity of one substance based on the quantity of another, you must multiply by the molar ratio (unknown / known)

How many moles of HNO 3 are produced when 0.50 moles of N 2 O 5 react as follows: N 2 O 5 + H 2 O  2 HNO 3

Lead reacts with HCl to produce lead(II) chloride and hydrogen. How many moles of HCl are needed to completely react with 0.36 moles of Pb? Pb + 2HCl  PbCl 2 + H 2

How many moles of water will be produced if 2.35 moles of oxygen react with benzene (C 6 H 6 )? 2C 6 H 6 +15O 2  12CO 2 + 6H 2 O

Solving Stoich. Problems: balanced equation convert known quantity to moles calculate molar ratio convert unknown from # moles to units

How many moles of NaBr will be produced when 0.69 moles of bromine react? Br 2 +2NaI  2NaBr + I 2

Problem: What mass of chlorine is needed to react with 1.25 mol TiO 2 ? TiO 2 +C+2Cl 2 → TiCl 4 +CO mol TiO 2 2 mol Cl 2 71 g Cl 2. 1 mol TiO 2 1 mol Cl 2 = g Cl 2

Problem: What mass of chlorine gas can be obtained from 2.5 mol NaCl when it decomposes? 2.5 mol NaCl 1 mol Cl 2 71 g Cl 2. 2 mol NaCl 1 mol Cl 2 = g Cl 2 2 NaCl  2 Na + Cl 2

Determine the mass of zinc chloride produced when 5.3 grams of Zn react with hydrochloric acid (HCl). Problem:

Mass to mass steps: convert known mass to moles [÷ molar mass]. Use molar ratio to calc. moles unknown [x molar ratio: Unknown / known] convert unknown to grams [x molar mass unknown]

Calculations : Every number has 2 labels: units [g, L, mol..] substance [H 2, NaCl..]

Determine the mass of lithium hydroxide produced when 0.38 g. lithium nitride reacts with water. (The other product is ammonia.) Problem:

4NH 3 + 6NO → 5N 2 + 6H 2 O Identify all molar ratios for the equation above. How much NO is needed to produce 8 mol N 2 ?

2Al + Fe 2 O 3 → Al 2 O 3 + 2Fe How many moles Fe produced for each mole iron(III) oxide used? 2

Molar Volume: The volume of 1 mole of a gas. =22.4 L/mole at STP (0º C & 1 atm)

STP (for gases): Standard Temperature and Pressure: T = 0 °C = 273 K P = 1 atmosphere

Problem: 16.0 g. of O 2 reacts with 2.0 g. of H 2. The volume of H 2 = 22.4 L. What is the volume of the O 2 ? 11.2 L

Problem: If you have 3.25 moles of He gas at STP, what volume does it occupy? 3.25 mole 22.4 L 1 mole = 72.8 L

Find the following: 1. # moles of air in a 893 L container at STP 2. vol moles N 2 gas would occupy at STP? 3. # molecules CO in a 10 mL test tube at STP

Problem: How many grams of CO 2 are in a 1.0 L balloon at STP? g

Mole Bridge KnownUnknown Mass Mass ÷ molar mass x molar mass Volume ÷22.4 mol unknown x 22.4 Vol. mol known ÷ 6.02 x 10E23 x 6.02x10E23 # atoms

8 cheeseburgers Cheeseburgers:  12 hamburger buns  8 all-beef patties  15 pickles  9 slices cheese

10 S’Mores S’Mores:  21 graham cracker sqs  15 marshmallows  16 squares chocolate

NaHCO 3 NaHCO 3 + HCl → NaCl + CO 2 + H 2 O

Limiting Reactant:  The reactant that is used up completely in a reaction  this “limits” the quantity of product

Find the limiting reactant when 3.6 mol Al react with 5.0 mol Cl 2 to form AlCl 3 Problem

Find Limiting Reactant:  Calculate the quantity of product formed from the given quantity of a reactant.  repeat for given quantities of other reactant(s).

Find L. R. (cont.):  Compare the quantities of products formed.  The reactant that produces the smallest amount of product is the limiting reactant.

If 2.6 g. of hydrogen is combined with 10.2 g. oxygen, what mass of water will be produced? Problem

Find moles that do react: mol product x reactant coef. product coef. Subtract this from original quantity to find excess. Excess reactant

Find the limiting reactant when 15.2 moles P react with 18.0 moles O 2 to form P 4 O 10 Problem:

Theoretical Yield:  The quantity of product you expect to get.

Actual Yield:  The quantity of product you actually get.

Percent Yield: = 100 (actual yield) (theoretical yield)

One lab group had an actual yield of 1.62 g. NaCl when they expected to get 2.09 g. NaCl. What is their percent yield? 77.5% Problem