Types of Chemical Reactions - Dr Cook's ChemistryDecomposition Reactions Types of decomposition...
Transcript of Types of Chemical Reactions - Dr Cook's ChemistryDecomposition Reactions Types of decomposition...
Types of Chemical Reactions
Writing Chemical Reactions
Types of Reactions
Many chemical reactions have defining characteristics which allow them to be classified as to type.
Types of Chemical Reactions
The five types of chemical reactions in this unit are:
Synthesis
Decomposition
Single Replacement
Double Replacement
Combustion
Synthesis Reactions
Two or more substances combine to form one substance.
The general form is A + X AX
Example:
Magnesium + oxygen magnesium oxide
2Mg + O2 2MgO
Synthesis Reactions
Synthesis reactions may also be called composition or combination reactions.
Some types of synthesis reactions:
Combination of elements
One product will be formed from multiple reactants
Synthesis Reactions
K + Cl2
Write the ions: K+ Cl-
Balance the charges: KCl
Balance the equation: 2K + Cl2 2KCl
Synthesis Reactions
Some types of synthesis reactions:
Oxides + water
Nonmetal oxide + water acid (don’t
need to memorize this)
SO2 + H2O H2SO3
Metal oxide + water metal
hydroxide (base)
BaO + H2O Ba(OH)2
Synthesis Reactions
Some types of combination reactions:
Metal oxides + nonmetal oxides
Na2O + CO2 Na2CO3
CaO + SO2 CaSO3Notice how the oxygens simply add together
Decomposition Reactions
One substance reacts to form two or more substances.
The general form is AX A + X
Example:
Water can be decomposed by electrolysis. (-lysis means “to split”)
2H2O 2H2 + O2
Decomposition Reactions
Types of Decomposition Reactions:
Decomposition of carbonates
When heated, some carbonatesbreak down to form an oxide and carbon dioxide.
CaCO3 CaO + CO2
H2CO3 H2O + CO2
Decomposition Reactions
Types of decomposition reactions:
Some metal hydroxides decompose into oxides and water when heated.
Ca(OH)2 CaO + H2O
Note that this is the reverse of a similar combination reaction.
Decomposition Reactions
Types of decomposition reactions: Metal chlorates decompose into
chlorides and oxygen when heated.
2KClO3 2KCl + 3O2
Zn(ClO3)2 ZnCl2 + 3O2
Some of these reactions are used in explosives.
Decomposition Reactions
Some substances can easily decompose: Ammonium hydroxide is actually
ammonia gas dissolved in water.
NH4OH NH3 + H2O
Some acids decompose into water and an oxide. (don’t need to memorize this)
H2SO3 H2O + SO2
Combustion Reaction
When a substance combines with oxygen, a combustion reaction results.
The combustion reaction may also be an example of an earlier type such as 2Mg + O2 2MgO (synthesis)
Combustion Reactions
Combustion reactions involve light and heat energy released.
Natural gas, propane, gasoline, etc. are burned to produce heat energy.
Most of these reactions with hydrocarbons produce water and carbon dioxide.
Combustion Reaction
Methane, CH4, is natural gas.
When hydrocarbon compounds are burned in oxygen, the products are water and carbon dioxide.
CH4 + O2 CO2 + H2O
CH4 + 2O2 CO2 + 2H2O
Single Replacement Reactions
A metal will replace a metal ion in a compound. The general form is A + BX AX + B
A nonmetal will replace a nonmetal ion in a compound. The general form is Y + BX BY + X
Look for an element + a compound as reactants
Single Replacement Reactions
Examples:
Ni + AgNO3
Nickel replaces the metallic ion Ag+.
The silver becomes free silver and the nickel becomes the nickel(II) ion.
Ni + AgNO3 Ag + Ni(NO3)2
Balance the equation:
Ni + 2AgNO3 2Ag + Ni(NO3)
Single Replacement Reactions
Not all single replacement reactions that can be written actually happen.
The free metal must be more active than the metal ion it is replacing.
You can use the activity series to predict if a single replacement reaction will occur.
Elements at the top will replace elements below.
Single Replacement Reactions
An active nonmetal can replace a less active nonmetal.
The halogen (F2, Cl2, Br2, I2) reactions are good examples.
F2 is the most active and I2 is the least.
Cl2 +2 NaI 2 NaCl + I2
Predicting Single Replacements
Use the activity series to predict the outcome:
Ag + CuCl2
K + NaCl
Cl2 + NaI
I2 + KBr
Predicting Single Replacements
Use the activity series to predict the outcome:
Ag + CuCl2 No reaction
K + NaCl KCl + Na
Cl2 + NaI I2 + NaCl
I2 + KBr No reaction
Double Replacement Reactions
Ions of two compounds exchange places with each other. The general form is AX + BY AY + BX
Look for two ionic compounds (this includes acids + bases)
Often the driving force is the formation of a solid (precipitate), which we can predict with solubility rules
Double Replacement
CuSO4(aq)+ Na2CO3(aq)
Cu2+ combines with CO32- to form
CuCO3, which is a solid
Na+ combines with SO42- to form
Na2SO4, which remains dissolved.CuSO4(aq)+ Na2CO3(aq) CuCO3(s)+ Na2SO4 (aq)
Double Replacement
A special type of double replacement involves acids reacting with bases. It is called a neutralization.
The general format:Acid (H in front) + base (OH in back) salt + H2O
Double Replacement -Neutralizations
Example: Hydrochloric acid + sodium hydroxide
HCl + NaOH
HCl + NaOH NaCl + H2O
The Na+ and Cl- ions combine to make NaCl
The H+ from the acid combines with OH- from the base to make water (H2O or HOH)
Practice
Classify each of the following as to type:
H2 + Cl2 2HCl
Combination
Ca + 2H2O Ca(OH)2 + H2
Single replacement
Practice
2CO + O2 2CO2
Combination and combustion
2KClO3 2KCl + 3O2
Decomposition
Practice
FeS + 2HCl FeCl2 + H2S
Double replacement
Zn + HCl ?
Single replacement
Zn + 2HCl ZnCl2 + H2