Chapters 6 – 7 Chemical Reactions
Dec 31, 2015
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
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)
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)