Chapters 6 – 7Chemical Reactions

Evidence for a Chemical Reaction

Change in ColorHair changes color when it is bleached

A blue flame appears when natural gas reacts with oxygen

Formation of a Precipitate (Solid)A yellow solid forms when a solution of KI reacts with Pb(NO3)2

Nylon is formed when two particular liquid solutions are combined

Production of GasBubbles of hydrogen gas form when calcium metal reacts with water

H2 and O2 gas form when an electric current is used to decompose water

Heat / Light is Produced – Heat is AbsorbedA bright white flame is produced when magnesium metal burns

Oxygen from the air penetrates the solid chemicals in the pouch of foot warmers – the reaction produces heat for several hours

Chemical Equations - any change in which one or more

substances are converted into different substances with different characteristic properties

Reactants –

Products –

Reactants → Product

http://www.youtube.com/watch?v=Mx5JJWI2aaw

Writing Chemical EquationsChemical Equation -

Chemical Equations Contain Useful InformationFormulas – the reactants and products are written with their correct

chemical formulasPhases – a symbol which expresses the state of the substance, is often

included to the right of the formula (written in parentheses)

Amounts – relative numbers of reactant and product molecules that are required (coefficients)

Sample Chemical Reaction

Balancing Chemical Equations

Conservation of Matter•Matter cannot be created or destroyed.

•In a chemical reaction, all the atoms present at the beginning are still present at the end.

•Reactions involve rearrangement and exchange of atoms to produce new molecules.

•The total mass cannot change.

CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (l)

Balancing Chemical EquationsLiNO3 LiNO2 + O2

BaO + P2O5 Ba3(PO4)2

CaCO3 CaO + CO2

MnSO4 + K3PO4 Mn3(PO4)2 + K2SO4

Al(OH)3 + H2SO4 Al2(SO4)3 + H2O

C8H18 + O2 CO2 + H2O

SiF4 + H2O H2SiF6 + H2SiO3

Synthesis (Combination) –

The starting materials can be elements or compounds but the product must be a compound.

2 Na + Cl2 → 2 NaCl

H2 + F2 → 2 HF

MgO + H2O → Mg(OH)2

Types of Reactions

Types of ReactionsDecomposition –

2 Al2O3 → 4 Al + 3 O2

2 KNO3 → 2 KNO2 + O2

The starting material must be a compound. The products can be either elements or compounds.

Decomposition reactions require energy:

Types of ReactionsSingle-Replacement –

-reactants and products always include one element and one compound

2 Al + 3 Fe(NO3)2 → 3 Fe + 2 Al(NO3)3

F2 + 2 HCl → 2 HF + Cl2

Halogens

fluorinechlorinebromineiodine

Predict the products of the following single-replacement reactions. If no product exist write NAR for no apparent reaction.

Zn(s) + HCl(aq) →

Na(s) + H2O(l) →

Sn(s) + AlCl3(aq) →

Cu(s) + AgNO3(aq) →

F2(g) + HBr(aq) →

Types of ReactionsDouble-Replacement –

One of the products must be a:

Pb(NO3)2 (aq) + 2 KI (aq) → PbI2 (s) + 2 KNO3 (aq)

FeS (s) + 2 HCl (aq) → H2S (g) + FeCl2 (aq)

HCl (aq) + NaOH (aq) → NaCl (aq) + H2O (l)

Double Replacement ReactionsHow do you know if a precipitate forms?

One or more of the products must be insoluble in water (this means that the substance does NOT dissolve in water).

Learn and use the KISS Guidelines!!!

Keep It Simple Solubility

All salts containing (insert any ion from Guidelines 1-4) are soluble

Cation Guideline:

1. Na+, NH4+, K+

Anion Guidelines:

2. NO3-, C2H3O2

-, ClO3-, ClO4

-

 3. Halides (Cl-/Br-/I-) except when paired with Ag+, Hg2

2+, Pb2+

 4. SO4

2- except when paired with Ag+, Hg22+, Pb2+, Ba2+

and Sr2+

KISS Guidelines

The “Catch-all” Guideline:

5. Everything else is assumed to be insoluble.

Soluble or Insoluble?manganese(II) chloride

lead(II) sulfate

potassium fluoride

magnesium sulfate

sodium carbonate

chromium(III) hydroxide

ammonium sulfide

zinc(II) phosphate

silver(I) chloride

Predict the identity of the precipitate that forms when aqueous solutions of the following substances are mixed. If no precipitate is likely, indicate which rules apply.

FeCl3 + H3PO4 →

K2SO4 + Ca(C2H3O2)2 →

Na2CO3 + MnCl2 →

KOH + NiCl2 →

(NH4)2S + MgCl2 →

Ba(NO3)2 + H2SO4 →

AgNO3 + CaBr2 →

Double Replacement Reactions

How do you know if a gas forms? Learn the following compounds and recognize them as gases or “phantom” gases.

hydrogen sulfide – H2S (g)

hydrogen cyanide – HCN (g)

carbonic acid – H2CO3

sulfurous acid – H2SO3

ammonium hydroxide – NH4OH

Predict the products of the following reactions.

HCl (aq) + K2SO3 (aq) →

NaOH (aq) + NH4Cl (aq) →

HCl (aq) + Na2S (aq) →

H2SO4 (aq) + KCN (aq) →

HCl (aq) + NaHCO3 (aq) →

Double Replacement ReactionsAcid-Base Reactions

Neutralization Reactions

The products of an acid-base reaction are

STRONG ACID + STRONG BASE → HOH + “salt”

HCl + NaOH → HOH + NaCl

A “salt” is defined as an ionic compound.

Acids• Acid comes from the Latin word “acidus” which means

sour.• In the 1800’s, Svante Arrhenius discovered the essential

nature of acids.– He observed that when the substances HCl, HNO3, and H2SO4

were dissolved in water, they behaved as strong electrolytes (they conducted electricity well)

– He suggested that this was the result of ionization.

HCl + H2O → H+ (aq) + Cl- (aq)

HNO3 + H2O → H+ (aq) + NO3- (aq)

H2SO4 + H2O → H+ (aq) + HSO4- (aq)

Strong Acids

Strong acids –

Learn the following strong acids.

Bases• Arrhenius also found that aqueous solutions that

exhibit basic behavior always contain hydroxide ions (OH-).

• Learn the strong bases:

Acid-Base Reactions

Strong Acid + Strong Base → Water + A “salt”

HBr(aq) + NaOH(aq) → HOH(l) + NaBr(aq)

HNO3(aq) + KOH(aq) →

Ba(OH)2(aq) + HCl(aq) →

Combustion Reactions

Combustion –

-the burning of natural gas, wood, and propane are examples

-when hydrocarbons burn completely, they form carbon dioxide and water

-hydrocarbons are compounds composed of carbon and hydrogen

Methane CH4

Ethane C2H6

Propane C3H8

Butane C4H10

Pentane C5H12

HexaneC6H14

Heptane C7H16

Octane C8H18

NonaneC9H20

DecaneC10H22

C3H8 (g) + O2 (g) → CO2 (g) + H2O (g)

CH4 (g) + O2 (g) → CO2 (g) + H2O (g)