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Chemical Reactionsreactants products
Balancing chemical equationsTypes of chemical reactions
How reactants are transformed into products?
• Reactants are transformed during chemical reactions
• Energy is required (absorbed) to break a chemical bond
• Energy is released when a chemical bond forms
Balancing equations
• Obey law of conservation of matter• Chemical equations have two
parts: reactants and products
How to balance?
• The total number of atoms of each element should be the same on both sides of equation
• Use coefficients to balance equations
Example:
2H2 + O2 2 H2O
Types of chemical reactions
• Single replacement• Double replacement• Decomposition• Combination • Combustion
Synthesis (Combination) Synthesis (Combination) ReactionsReactions
Two or more substances combine to form a new compound.
A + X AX
Reaction of elements with oxygen and sulfur Reactions of metals with Halogens Synthesis Reactions with Oxides There are others not covered here!
Decomposition Decomposition ReactionsReactions
A single compound undergoes a reaction that produces two or more simpler substances
Decomposition of: Binary compounds 2H2O(l ) 2H2(g) +
O2(g) Metal carbonates CaCO3(s) CaO(s) +
CO2(g) Metal hydroxides Ca(OH)2(s) CaO(s) +
H2O(g) Metal chlorates 2KClO3(s) 2KCl(s) +
3O2(g) Oxyacids H2CO3(aq) CO2(g) +
H2O(l )
AX A + X
Decomposition ReactionsSulfatesWith the exception of alkali metals and alkaline sulfates, all other metals are decomposed by heat to form a metal oxideNitrates Alkali metals decompose on heating to yield the nitrites and oxygen. All other metal nitrates are decomposed to nitrogen dioxide, oxygen, and the metal oxide on heating.
Single Replacement Single Replacement ReactionsReactions
Replacement of:
Metals by another metal Hydrogen in water by a metal Hydrogen in an acid by a metal Halogens by more active halogens
A + BX AX + B
BX + Y BY + X
The Activity Series of the The Activity Series of the MetalsMetals
Lithium Potassium Calcium Sodium Magnesium Aluminum Zinc Chromium Iron Nickel Lead Hydrogen Hydrogen Bismuth Copper Mercury Silver Platinum Gold
Metals can replace other metals provided that they are above the metal that they are trying to replace.
Metals above hydrogen can replace hydrogen in acids.
Metals from sodium upward can replace hydrogen in water
Mg + AlCl3
Al + MgCl2
Predict if these reactions will occurAl + MgCl2
Can magnesium replace aluminum?
Activity Series
YES, magnesium is more reactive than aluminum.
2 23 3
Can aluminum replace magnesium?
Activity Series
NO, aluminum is less reactive than magnesium.
Therefore, no reaction will occur.
No reaction
MgCl2 + Al No reaction
The question we must ask is can the single element replace its counterpart? metal replaces metal or nonmetal replaces nonmetal.
Order of reactants DOES NOT
determine how they react.
The Activity Series of the The Activity Series of the HalogensHalogens
Fluorine Chlorine Bromine Iodine
Halogens can replace other halogens in compounds, provided that they are above the halogen that they are trying to replace.
2NaCl(s) + F2(g) 2NaF(s) + Cl2(g)
MgCl2(s) + Br2(g) ???No Reaction
???
Single Replacement Reactions• Sodium chloride solid reacts with fluorine gas
NaCl(s) + F2(g) NaF(s) + Cl2(g)
Note that fluorine replaces chlorine in the compound
• Aluminum metal reacts with aqueous copper (II) nitrate
Al(s)+ Cu(NO3)2(aq) Cu(s) + Al(NO3)3(aq)
2 2
2 3 3 2
Double Replacement ReactionsDouble Replacement Reactions
The ions of two compounds exchange places in an aqueous solution to form two new compounds.
AX + BY AY + BX
One of the compounds formed is usually a precipitate, an insoluble gas that bubbles out of solution, or a molecular compound, usually water.
Double Replacement Reactions
• Think about it like “foil”ing in algebra, first and last ions go together + inside ions go together
• Example:
AgNO3(aq) + NaCl(s) AgCl(s) + NaNO3(aq)
• Another example:
K2SO4(aq) + Ba(NO3)2(aq) KNO3(aq) + BaSO4(s) 2
Combustion ReactionsCombustion ReactionsA substance combines with oxygen, releasing a large amount of energy in the form of light and heat.
Reactive elements combine with oxygen
P4(s) + 5O2(g) P4O10(s)
(This is also a synthesis reaction)
The burning of natural gas, wood, gasoline
C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(g)
Solubility and precipitation reactions
Pb(NO3)2 (aq) + 2NaI(aq) PbI2(s) + 2NaNO3(aq)
FeCO3
Na1+Fe2+
iron (II) chloride + sodium carbonate
Cl2
Using a SOLUBILITY TABLE:sodium chloride is soluble
iron (II) carbonate is insoluble
CO3
Fe2+
Fe
Na1+
Na2
Cl1- CO32- Cl1- CO3
2-
NaCl
sodium chloride iron (II) carbonate+
(aq) (ppt)
2FeCl2 Na2CO3 NaCl FeCO3(aq) (ppt)+ +
Predict if a reaction will occur when you combine aqueous solutions of iron (II) chloride with aqueous sodium carbonate solution.
If the reaction does occur, write a balanced chemical equation showing it.
(be sure to include phase notation)
(aq) (aq)
Balanced chemical equation
Complete Ionic EquationFe2+(aq) + 2Cl1-(aq) + 2Na1+(aq) + CO3
2-(aq) 2Na1+(aq) + 2Cl1-(aq) + FeCO3(s)
Solubility rules
Soluble in water: • sodium, potassium, and ammonium
salts; acetates and nitrates• Halides with the exception of halides
of lead (II), silver(I), and mercury(I).• Sulfates with the exception of
sulfates of calcium, barium, lead (II) and strontium
Insoluble in water
• Phosphates, carbonates and sulfides except sodium, potassium, ammonium salts, and calcium sulfide
• Hydroxides except sodium, potassium, calcium, and barium hydroxides
Acid-Base reactions(neutralization reactions)
• Acid: any compound that produces hydrogen ions (H+), when added to water.
• Base: any substance that produces hydroxide ions (OH-), when added to water.
HCl(aq) + Na(OH)(aq) NaCl(aq) + H2O(l)