8:35 PM Unit 1: Stoichiometry Chemistry 2202. 8:35 PM Stoichiometry Stoichiometry deals with quantities used in OR produced by a chemical reaction

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Unit 1: Stoichiometry

Chemistry 2202

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Stoichiometry

Stoichiometry deals with quantities used in OR produced by a chemical reaction

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3 Parts

Mole Calculations (Chp. 2 & 3) Stoichiometry and Chemical

Equations (Chp. 4) Solution Stoichiometry (Chp. 7/8)

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PART 1 - Mole Calculations

Isotopes and Atomic Mass (pp. 43 - 46)

Avogadro’s number (pp. 47 – 49) Mole Conversions (pp. 50 - 74)

M, MV, NA, n, m, v, N

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PART 1 - Mole Calculations

Percent composition: - given mass (p. 79 - 82) - given the chemical formula (p. 83 - 86)

Empirical Formulas (pp. 87 - 94) Molecular Formulas (pp. 95 - 98) Lab: Formula of a Hydrate

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Chapter 2 Isotopes and Atomic Mass

atomic number - the number of protons in an atom or ion

mass number - the sum of the protons and neutrons in an atom

isotope - atoms which have the same number of protons and electrons but different numbers of neutrons

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Isotopes and Atomic Mass eg.

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Isotope NotationIsotope Name

C12

6

Carbon - 12

mass number atomic number

Isotope NotationIsotope Name

C14

6

Carbon - 14

mass number atomic number

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Isotopes and Atomic Mass

1735

1737C l C l

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1224

1225

1226M g M g M g

not all isotopes are created equal

79 % 10 % 11 %

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atomic mass unit (AMU - p.43)- a unit used to describe the mass of

individual atoms- the symbol for the AMU is u- 1 u is 1/12 of the mass of a carbon-12

atom

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average atomic mass (AAM)- the AAM is the weighted average of

all the isotopes of an element (p. 45)

Example: Copper, a metal known since ancient times, is used in electrical cables and pennies. The atomic masses of its two stable isotopes, copper- 63 (69.09%) and copper- 65 (30.91%), are 62.93 amu and 64.9278 amu, respectively. Calculate the average atomic mass of copper.

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Finding % Abundance

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Finding % Abundance

ex. Br has two naturally occurring isotopes. Br-79 has a mass of 78.92 u and Br-81 has a mass of 80.92 u. If the AAM of Br is 79.90 u, determine the percentage abundance of each isotope.

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Let x = fraction of Br-79Let y = fraction of Br-81

x + y = 178.92x + 80.92y = 79.90

Finding % Abundance

y = 1 - x

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x + y = 178.92x + 80.92y = 79.90

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Avogadro’s Number (p. 47)

p. 48

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Avogadro’s Number The MOLE is a number used by chemists to

count atoms The MOLE is the number of atoms contained in

exactly 12 g of carbon-12. In honor of Amedeo Avogadro, the number of

particles in 1 mol has been called Avogadro’s number.

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How big is Avogadro's number?

An Avogadro's number of soft drink cans would cover the surface of the earth to a depth of over 200 miles.

Avogadro's number of unpopped popcorn kernels spread across the USA, would cover the entire country to a depth of over 9 miles.

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If we were able to count atoms at the rate of 10 million per second, it would take about 2 billion years to count the atoms in one mole.

How big is Avogadro's number?

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Avogadro’s Number

1 mole = 6.02214199 x 1023 particles

1 mol = 6.022 x 1023 particles

NA = 6.022 x 1023 particles/mol

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Avogadro’s Number

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Avogadro’s Number

Number of moles Number of atoms

5 mol

0.01 mol

4.65 x 1024 atoms

8.01 x 1021 atoms

7.72 mol

0.0133 mol

6.022 x 1021 atoms

3.011 x 1024 atoms

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Avogadro’s Number

Formulas:

AN

Nn n = # of moles

N = # of particles (atoms, ions, molecules, or formula units)

NA = Avogadro’s #

N = n x NA

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How many moles are contained in the following?

a) 2.56 x 1028 Pb atoms

b) 7.19 x 1021 CO2 molecules

Avogadro’s Number

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Avogadro’s Number

eg. Calculate the number of moles in 4.98 x 1025 atoms of Al.

eg. How many formula units of Na2SO4 are in 5.69 mol of Na2SO4?

# of Na ions? # of Oxygen atoms?

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Avogadro’s Number

1. How many molecules of glucose are in 0.435 mol of C6H12O6?

How many carbon atoms?2. Calculate the number of moles in

a sample of glucose that has 3.56 x 1022 hydrogen atoms.

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Molar Mass

The mass of one mole of a substance is called the molar mass of the substance

eg. 1 mole of Pb has a mass of 207.19 g1 mole of Ag has a mass of 107.87 g

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Molar Mass

The symbol for molar mass is M and the unit is g/mol

eg. MPb = 207.19 g/mol

MAg = 107.87 g/mol

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Molar Mass

The molar mass of a compound is the sum of the molar masses of the elements in the compound

eg. Calculate the molar mass of:a) H2O b) C6H12O6 c) Ca(OH)2

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Molar Mass

H2O

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Molar Mass

C6H12O6

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Molar Mass

Ca(OH)2

Your calculator may not show the zeroes.There should be 2 digits after the decimal when adding molar masses

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Molar Mass Calculations

AN

Nn

M

mn

N = n x NA

mass

molar

mass

m = n x M

Avogadro’s #

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AN

Nn

M

mn

N = n x NA

m = n x M

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eg. How many moles are in 25.3 g of NO2?

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eg. What is the mass of 4.69 mol of water?

particles(N)

Moles(n)

Mass(m)

5.98 x 1026 Cu atoms

4.50 g H2O

6.15 mol O3

Particle–Mole-Mass Conversions

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moles (n)

mass (m)

particles(N)

x M

÷ M÷ NA

x NA

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eg. How many molecules are in 26.9 g of water?

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eg. How many molecules are in 4.78 g of glucose?

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eg. A sample of Sn contains 4.69 x 1028 atoms. Calculate its mass.

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Molar Volume

•The volume of a gas increases when temperature increases but decreases when pressure increases .

•The volume of gases is measured under conditions of Standard Temperature and Pressure (STP)

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Molar Volume

Standard Pressure – 101.3 kPa Standard Temperature – 0 °C Avogadro hypothesized that equal

volumes of gases at the same temperature and pressure contain equal numbers of molecules.

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Molar Volume

Experimental evidence shows the volume of one mole of ANY GAS at STP is 22.4 L/mol

OR VSTP = 22.4 L/mol

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AN

Nn

M

mn

N = n x NA

m = n x M

STPV

vn

v =n x VSTP

given volume in Litres

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moles (n)

mass (m)

particles(N)

x M

÷ M÷ NA

x NA

volume (v)

x VSTP÷ VSTP

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Chapter 3Percent Composition (p. 79)

The mass percent of a compound is the mass of an element in a compound expressed as a percent of the total mass of the compound.

mass percen tm ass o f elem en t

to ta l m ass o f com poundX 100%

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Percent Composition

eg. 8.50 g of a compound was analyzed and found to contain 6.00 g of hydrogen and 2.50 g of carbon. Calculate the mass percent for each element.

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Percent Composition

mass percent may be found using the formula & the molar mass of a compound.

eg. Find the percentage composition for CH4

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Percent Composition

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Empirical Formulas

An empirical formula gives the simplest ratio of elements in a compound.A molecular formula shows the actual number of atoms in a molecule of a compound.Ionic compounds are always written as empirical formulas

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Empirical Formulas

Compound Molecular Formula

Empirical Formula

butane C4H10

glucose C6H12O6

water H2O

benzene C6H6

C2H5

CH2O

H2O

CH

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Empirical Formulas (p.87)

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Empirical Formulas

The empirical formula of a compound may be determined by using the % composition of a given compound.

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Empirical Formulas

Method: assume you have 100.0 g of the

compound (ie. change % to g) calculate the moles (n) for each

element divide each n by the smallest n to get

the ratio for the empirical formula

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Empirical Formulas

eg. A compound was analyzed and found to contain 87.4% N and 12.6 % H by mass. Determine the empirical formula of the compound.

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Empirical Formulas

When finding the EF, the mole ratio may not be a whole number ratio.

eg. A compound contains 84.73% N and 15.27 % H by mass. Determine the empirical formula of the compound.

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Empirical Formulas

eg. A compound contains 89.91% C and 10.08 % H by mass. Determine the empirical formula of the compound.

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Molecular Formulas The molecular formula of a compound is

a multiple of the empirical formula.

See p. 95

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Molecular Formulas

To find the molecular formula we need the empirical formula and the molar mass of the compound

eg. The empirical formula of hydrazine is NH2. The molar mass of hydrazine is 32.06 g/mol. What is the molecular formula for hydrazine?

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Example : An unknown was subjected to a combustion analysis and found to be 85.60% carbon and 14.40% hydrogen. Mass spectrometry indicated that its molar mass was 28.06 g/mol. Determine the molecular formula of the compound.

Molecular Formulas

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CHC analyzer (p. 99 – 101)

1. Describe the operation of a carbon hydrogen combustion analyzer.

2. 22.0 g of carbon dioxide and 10.8 g of water is collected in a CHC analysis. Determine the empirical formula of the hydrocarbon.

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Formula of a hydrate

To determine the formula of a hydrate:

- calculate the moles of water

- calculate the moles of anhydrous compound

- determine the simplest ratio

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Formula of a hydrate

eg. Use the data below to determine the value of x in LiCl• xH2O.

mass of crucible = 26.35 g

crucible + hydrate = 42.15 g

crucible + anhydrous compound= 34.94 g

mwater = 42.15 – 34.94 = 7.21 g H2O

mLiCl = 34.94 – 26.35 = 8.59 g LiCl

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eg. Na2CO3. xH2O

crucible = 15.96 g

crucible + hydrate = 22.19 g

crucible + anhydrous compound = 19.67 g

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eg. CoCl2.xH2O

crucible = 151.96 gcrucible + hydrate = 164.35 g crucible + anhydrous compound =

158.23 g

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Chapter 4 Stoichiometry

Stoichiometry is the determination of quantities needed for, or produced by, chemical reactions.

Can be gravimetric (mass), gas (Vstp), or solution stoichiometry (solutions)

Ratios from balanced chemical equations are used to predict quantities.

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Stoichiometry – p. 111

Clubhouse sandwich recipe

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Clubhouse sandwich recipe

Slices of Toast

Slices of Turkey

Strips of Bacon

# of Sandwiche

s

12

27

66

100

Fill in the missing quantities:

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Mole Ratios

A mole ratio is a mathematical expression that shows the relative amounts of two species involved in a chemical change.

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Mole Ratios

A mole ratio Come from a balanced chemical equation Shows the relative amounts of the

reactants/products in moles Is the coefficient for the required species

in the numerator and the coefficient for the given species in the denominator. (What you WANT over what you GOT)

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N2(g) + 3 H2 (g) → 2 NH3 (g)

20

66

140

81

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C3H8 + 5 O2 → 3 CO2 + 4 H2O

# #required given xcoeffic ien t

coeffic ien trequired

given

How many moles of CO2 are produced when 31.5 mol of O2 react?

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C3H8 + 5 O2 → 3 CO2 + 4 H2O



given

How many moles of H2O are produced when 1.35 mol of O2 react?

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C3H8 + 5 O2 → 3 CO2 + 4 H2O



given

How many moles of O2 are needed to produce 31.5 mol of CO2?

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C3H8 + 5 O2 → 3 CO2 + 4 H2O



given

How many moles of C3H8 are needed to react with 0.369 mol of O2?

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C5H12 + O2 → CO2 + H2O



given

How many moles of CO2 are produced when 6.35 mol of O2 react?

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Al(s) + Br2(l) → AlBr3(s)



given

How many moles of Br2 are needed to produce 0.315 mol of AlBr3?

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Mole to Mole Stoichiometry

1. How many moles of nitrogen gas are needed to produce 6.75 mol of NH3 in a reaction with hydrogen gas? (3.38mol)

2. How many moles of silver would be produced if 10.0 mol of silver nitrate reacts with copper metal? (10.0 mol)

3. How many moles of water are produced when 20.6 mol of CH4 burns? (41.2mol)

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Mole to Mole Stoichiometry1. How many moles of copper would be

produced if 20.5 mol of copper (II) oxide decomposes? (20.5mol)

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Mass to Mole Stoichiometry

1. How many moles of water are produced when 20.6 g of CH4 burns? (2.56mol)

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Mass to Mole Stoichiometry

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Mass to Mass Stoichiometry

eg. Calculate the mass of HCl needed to react with 3.56 g of Fe to produce FeCl2. (4.63g)

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Mole to Mass Stoichiometry

1. What mass of CaCl2 is produced when 4.38mol of Ca(NO3)2 reacts with NaCl? (486g)2. How many moles of copper would be produced if 20.5 g of copper (II) oxide decomposes? (0.258 mol)3. How many moles of water are produced when 5.45 g of C3H8 burns? (0.496mol)

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Ca(NO3)2 + 2 NaCl → CaCl2 + 2 NaNO3

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2 CuO → 2 Cu + O2

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C3H8 + 5 O2 → 3 CO2 + 4 H2O

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Stoichiometry (Chp.4)

Four step stoichiometry:

1. Write a balanced chemical equation

2. Calculate moles given from mass

3. Mole ratio – find moles required

4. Calculate required quantity (mass)

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Stoichiometry (Chp.4)

eg. What mass of CO2 gas is produced when 45.9 g of CH4 burns ? (126g)

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eg. How many moles of HCl needed to react with 3.56 g of Fe to produce FeCl2. (0.127mol)

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Mole Calculations (p. 121 #13)

3.56 g ? mol

Fe + 2 HCl → FeCl2 + H2

How many moles of aluminum chloride can be produced from the reaction of chlorine and 10.8 mol of aluminum ? (10.8mol)

Cl2(g) + Al(s) → AlCl3(s)

How many moles of magnesium are needed to react with 27 g of iodine to form magnesium iodide? (0.11mol)

How many grams of nitrogen are needed to react with 14.0 mol of oxygen to produce nitrogen dioxide ? (196g)

1 N2(g) + 2 O2(g) → 2 NO2(g)

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Mole Calculations (p. 121 #14)

2.34 g ? L

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Limiting Reactant (p. 128)

1. 10.0 g of Li requires _______ of Br2

2. 15.0 g of Br2 requires _______ of Li

3. 10.0 g of Li produces _______ of LiBr4. 15.0 g of Br2 produces ______ of LiBr

This problem has _____ g of excess _____and will produce ______ g of LiBr

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10.0 g of Li reacts with 15.0 g of Br2. Calculate the mass of LiBr produced.

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The Limiting Reactant (LR) OR Limiting Reagent (LR) is the substance that is completely used in a chemical reaction.

The Excess Reactant is the reactant that is left over after a reaction is complete.

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eg. 2.00 g of NaI reacts with 2.00 g of Pb(NO3)2. Determine the LR and calculate the amount of PbI2 produced.

write a balanced equation find n for each reactant (Step #2) find moles produced by each

reactant (Step #3)

Pb(NO3)2 + 2 NaI → 2 NaNO3 + PbI2

2.00 g 2.00 g

What mass of calcium carbonate will be produced when 20.0 g of calcium phosphate reacts with 15.0 g of sodium carbonate?

(14.2 g)

What mass of barium hydroxide will be produced when 10.0 g of barium nitrate reacts with 30.0 g of sodium hydroxide? (6.56 g)

Ba(NO3)2 + 2 NaOH → 2 NaNO3 +Ba(OH)2

What volume of hydrogen gas at STP will be produced when 10.0 g of zinc metal reacts with 20.0 g of hydrogen chloride?

Zn + 2 HCl → H2 + ZnCl2

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Law of Conservation of Mass (p. 118)

In a chemical reaction, the total mass of reactants always equals the total mass of products.

eg. 2 Na3N → 6 Na + N2

When 500.00 g of Na3N decomposes 323.20 g of N2 is produced. How much Na is produced in this decomposition?

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Law of Conservation of Mass( p. 118)

eg. To produce 90.1 g of water, what mass of hydrogen gas is needed to react with 80.0 g of oxygen?

eg. If 3.55 g of chlorine reacts with exactly2.29 g of sodium, what mass of NaCl willbe produced?

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The theoretical yield is the amount of product that we calculate using stoichiometry

The actual yield is the amount of product obtained from a chemical reaction

Percent yield (p. 137)

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Percent yield (p. 137)

percent y ie ld actua l y ie ld

theoretica l y ie ld x 100

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8:35 PM Unit 1: Stoichiometry Chemistry 2202. 8:35 PM Stoichiometry Stoichiometry deals with quantities used in OR produced by a chemical reaction