The Arithmetic of The Arithmetic of ChemistryChemistryStoichiometry and chemical Stoichiometry and chemical reactionsreactions

3.7

3 ways of representing the reaction of H2 with O2 to form H2O

A process in which one or more substances is changed into one or more new substances is a chemical reaction

A chemical equation uses chemical symbols to show what happens during a chemical reaction

reactants products

Remember this?Remember this?

Law of mass conservationLaw of mass conservation Law of definite proportionsLaw of definite proportions

Balancing equationsBalancing equations

Number of atoms conserved: atoms in Number of atoms conserved: atoms in reactants equal to atoms in productsreactants equal to atoms in products Change coefficients, not subscriptsChange coefficients, not subscripts Balance atoms that occur in only one Balance atoms that occur in only one

reactant and one productreactant and one product Balance the restBalance the rest Check number of atoms on each sideCheck number of atoms on each side

Test yourselfTest yourself

Test yourself: ethane gas reacts with Test yourself: ethane gas reacts with oxygen gas to produce carbon dioxide and oxygen gas to produce carbon dioxide and waterwater

Heating potassium chlorate yields potassium Heating potassium chlorate yields potassium chloride and oxygen gaschloride and oxygen gas

Demo reaction: Pb(NODemo reaction: Pb(NO33))22 and KI and KI

Atoms: small scaleAtoms: small scale Macroscopic scale: the Macroscopic scale: the molemole

By definition: 1 atom 12C “weighs” 12 amu

On this scale

1H = 1.008 amu

16O = 16.00 amu

Atomic mass is the mass of an atom in atomic mass units (amu)

Average atomic masses: Average atomic masses: weighted averagesweighted averages

Natural lithium is:

7.42% 6Li (6.015 amu)

92.58% 7Li (7.016 amu)

The mole (mol) is the amount of a substance that contains as many entities as there

are atoms in exactly 12.00 grams of 12C

3.2

How Big is Avogadro’s How Big is Avogadro’s Number?Number?

an Avogadro’s number of softdrink cans an Avogadro’s number of softdrink cans would cover the surface of the earth to a would cover the surface of the earth to a depth of over 200 milesdepth of over 200 miles

if we were able to count atoms at the rate of if we were able to count atoms at the rate of 10 million per second, it would take about 2 10 million per second, it would take about 2 billion years to count an Avogadro’s number billion years to count an Avogadro’s number of atomsof atoms

Molar mass is the mass of 1 mole of in gramseggsshoes

marblesatoms

1 mole 12C atoms = 6.022 x 1023 atoms = 12.00 g

1 12C atom = 12.00 amu

1 mole 12C atoms = 12.00 g 12C

1 mole lithium atoms = 6.941 g of Li

For any element

atomic mass (amu) = molar mass (grams)

3.2

molecules

One Mole of:

C S

Cu Fe

Hg

3.2

Converting small scale to Converting small scale to large (and back)large (and back)

Dimensional analysis: Dimensional analysis: method of calculation utilizing a knowledge of units.

Conversion factors are used to manipulate units:

unit givenunit desired

factor Conversion

Test yourselfTest yourself

How many atoms are in 0.551 g of K?How many atoms are in 0.551 g of K?

How many molecules of water are in a How many molecules of water are in a 15g sample? How many individual H 15g sample? How many individual H atoms? O atoms?atoms? O atoms?

Back to chemical Back to chemical equationsequations

2H2H22 + O + O22 2H 2H22O can be read as:O can be read as: 2 molecules H2 molecules H2 2 of react with 1 molecule of Oof react with 1 molecule of O22

to produce 2 molecules of water, ORto produce 2 molecules of water, OR

2 moles of H2 moles of H22 react with 1 mole O react with 1 mole O22 to form 1 to form 1

mole of watermole of water Convert to grams.Convert to grams.

Limiting reagentLimiting reagent

6 green used up6 red left over

3.9

Do You Understand Limiting Reagents?

In one process, 124 g of Al are reacted with 601 g of Fe2O3

2Al + Fe2O3 Al2O3 + 2Fe

Calculate the mass of Al2O3 formed.

g Al mol Al mol Fe2O3 needed g Fe2O3 needed

OR

g Fe2O3 mol Fe2O3 mol Al needed g Al needed

124 g Al1 mol Al

27.0 g Alx

1 mol Fe2O3

2 mol Alx

160. g Fe2O3

1 mol Fe2O3

x = 367 g Fe2O3

Start with 124 g Al need 367 g Fe2O3

Have more Fe2O3 (601 g) so Al is limiting reagent3.9

General types of General types of simple chemical simple chemical reactionsreactions

1.1. Combination : A + Z Combination : A + Z AZ AZ

2.2. Decomposition: AZ Decomposition: AZ A + Z A + Z

3.3. Single replacement (substitution) Single replacement (substitution) A + BZ A + BZ AZ +B AZ +B

4.4. Double replacement/displacementDouble replacement/displacement

5.5. Neutralization (acids and bases)Neutralization (acids and bases)

6.6. Combustion: reaction with OCombustion: reaction with O22, energy , energy

producedproduced

1. Combination 1. Combination ReactionsReactions

Two or more substances (elements or Two or more substances (elements or compounds) react to produce one compounds) react to produce one compoundcompound

Also known as “synthesis” or “addition”Also known as “synthesis” or “addition” AA + + Z Z AZ AZ

MetalMetal oxygenoxygen metal oxidemetal oxide Nonmetal Nonmetal oxygenoxygen nonmetal oxidenonmetal oxide MetalMetal nonmetalnonmetal saltsalt WaterWater metal oxidemetal oxide basebase Metal oxideMetal oxide nonmetal oxidenonmetal oxide saltsalt

2. Decomposition2. Decomposition

ONE substance reacts to form two or more ONE substance reacts to form two or more substances (elements or compounds).substances (elements or compounds).

AZAZ A A + + ZZ CompoundCompound compound/elementcompound/element oxygenoxygen Metal carbonateMetal carbonate metal oxidemetal oxide carbon dioxidecarbon dioxide Hydrated saltHydrated salt saltsalt waterwater CompoundCompound compound/elementcompound/element waterwater

3. Single Replacement3. Single Replacement Also known as single displacement or substitution.Also known as single displacement or substitution. A metal (A) replaces a metal ion (B=metal) in its A metal (A) replaces a metal ion (B=metal) in its

salt or a hydrogen ion (B=H) in an acidsalt or a hydrogen ion (B=H) in an acid A + BZ A + BZ AZ +B AZ +B Ex. Fe(s) + CuSOEx. Fe(s) + CuSO44(aq) (aq) FeSO FeSO44(aq) + Cu(s)(aq) + Cu(s)

Ex. Sn(s) + HCl(aq) Ex. Sn(s) + HCl(aq) SnCl SnCl22(aq) + H(aq) + H22(g)(g)

A nonmetal (X) replacing another nonmetal (Z) in A nonmetal (X) replacing another nonmetal (Z) in its salt (B=metal) or acid (B=H)its salt (B=metal) or acid (B=H) ClCl22(g) + NaBr (aq) (g) + NaBr (aq) _____________________________ _____________________________

Bromine + Potassium Iodide Bromine + Potassium Iodide ____________________________________________

4. Double Replacement4. Double Replacement Also known as “Double displacement”, Also known as “Double displacement”,

“Metathesis”, or “Double decomposition.”“Metathesis”, or “Double decomposition.” Two compounds are involved with the cation of Two compounds are involved with the cation of

one compound EXCHANGING with the cation of one compound EXCHANGING with the cation of another compound.another compound.

AX + BZ AX + BZ AZ + BX AZ + BX These reactions proceed if one of the ff. is These reactions proceed if one of the ff. is

satisfied:satisfied:1.1. An insoluble/slightly soluble product is formed An insoluble/slightly soluble product is formed

(PRECIPITATE formation)(PRECIPITATE formation)2.2. A weakly ionized species is produced. The most A weakly ionized species is produced. The most

common species of this type is water.common species of this type is water.3.3. A gas is produced as a product.A gas is produced as a product.

5. Neutralization5. Neutralization

Reaction of an acid and a base that Reaction of an acid and a base that usually produces a salt and water.usually produces a salt and water.

HX + MOH HX + MOH MX + HOH MX + HOH Hydrochloric acid and sodium hydroxide.Hydrochloric acid and sodium hydroxide. Hydrochloric acid and magnesium hydroxide.Hydrochloric acid and magnesium hydroxide. Sulfuric acid and Barium hydroxideSulfuric acid and Barium hydroxide

To be discussed in a separate lessonTo be discussed in a separate lesson

6. Combustion6. Combustion Reactions involving oxygen (metal +oxygen), Reactions involving oxygen (metal +oxygen),

(nonmetal + oxygen), (organic compounds + (nonmetal + oxygen), (organic compounds + oxygen) are sometimes called oxygen) are sometimes called combustion reactions.combustion reactions.

Energy is given off in combustion reactions.Energy is given off in combustion reactions. For organic compounds, water and carbon dioxide For organic compounds, water and carbon dioxide

are usual byproducts.are usual byproducts. Ex. Metabolism of food, fuel combustion:Ex. Metabolism of food, fuel combustion:

Sucrose (CSucrose (C2222HH1212OO1111) combusts) combusts

Combustion of propaneCombustion of propane Combustion of hydrogenCombustion of hydrogen

QuizQuiz

Insoluble silver chloride is produced in Insoluble silver chloride is produced in the reaction between silver nitrate and the reaction between silver nitrate and hydrochloric acid.hydrochloric acid. What type of reaction is this?What type of reaction is this? Balance the equation.Balance the equation.

QuizQuiz

Sodium azide produces nitrogen gas and Sodium azide produces nitrogen gas and sodium metal. sodium metal. Type of reaction?Type of reaction? Balanced equation?Balanced equation? How many grams of nitrogen gas is How many grams of nitrogen gas is

produced from 60.0g sodium azide?produced from 60.0g sodium azide?

QuizQuiz

Working at 273.15K and 1atm (STP), I Working at 273.15K and 1atm (STP), I have 10.0g of carbon and 56L of oxygen. have 10.0g of carbon and 56L of oxygen. Under these conditions, I know 1mol of Under these conditions, I know 1mol of any gas has a volume of 22.4L (Molar any gas has a volume of 22.4L (Molar volume at STP). What is the limiting volume at STP). What is the limiting reagent? If carbon monoxide made sure reagent? If carbon monoxide made sure to be formed, what will be its volume?to be formed, what will be its volume?