Chemical Reactions
Chemical Reactions: CHAPTER 8
Chemical Reactions
-A process by which the atoms of one or more substance are rearranged to form different substances.
-Also known as a chemical change.
Signs of a Reaction
1.Temperature change
2. Color change
3. Odor
4. Precipitate is formed (solid)
5. Gas is formed
Types Reactions
-There are five main types of chemical reactions.
-They are classified based on how the atoms or groups of atoms are rearranged during the reaction.
-In a chemical reaction matter is not created or destroyed.
-Matter is rearranged into a different form. (Conservation of matter)
1. Synthesis (Combination)
-Two or more substances combine to form a new compound.
-The result is only one product.
-General Format:
A + B ( AB
Reactants Products
-Example:
2H2 + O2 (2H2O
2. Decomposition
-A single compound reacts to produce two or more new substances.
-Opposite of combination.
-General Format:
AB ( A + B
-Example:
2H2O (2H2 + O2
3. Single Replacement
-An element reacts with a compound replacing an element from it.
-A metal will only replace a metal.
-A nonmetal will only replace a nonmetal.
-Use the activity series to help determine if a single
replacement reaction occurs.
-General Format:
AB + C ( CB + A
-Example:
2HCl + Mg (2H2 + MgCl2
4. Double Replacement
-Ions of two compounds exchange places in an aqueous solution to form two
new compounds.
-An aqueous solution is a solution dissolved in water.
-In order for this reaction to occur a gas, a precipitate, or water is
formed.
-General Format:
AB + CD ( AD + CB
-Example:
Na2SO4 + Ba(NO3)2 ( 2NaNO3 + BaSO4 (s)
5. Combustion
-Oxygen combines with a hydrocarbon to produce water and carbon dioxide.
-A hydrocarbon is a compound that contains only carbon & hydrogen.
-General Format:
CxHy + O2 ( CO2 + H2O
Hydrocarbon
Examples:
Determine the type of reaction shown.
2Na3N ( 6Na + N2
2Na + Cl2 ( 2NaCl
CH4 + 2O2 (CO2 + 2H2O
2Li + 2H2O ( 2LiOH + H2
NH4NO3 (N2O + 2H2O
Fe + CuSO4 ( FeSO4 + Cu
CaCO3 ( CaO + CO2
Pb(NO3)2 + 2KI (PbI2 + 2KNO3
4Fe + 3O2 ( 2Fe2O3
CaCO3 + HCl (CaCl2 + H2CO3
Chemical Reactions
Chemical Equations
-An expression that uses chemical formulas & symbols o represent a chemical reaction.
Parts of Equations
-Two main parts compose chemical equations, reactants & products.
Parts of Equations
1. Reactants:
-Substances that undergoes a change
-Starting materials
-Written on the left side of the arrow
2. Products:
-New substances produced
-Ending materials
-Written on the right side of the arrow
Reactants (Products
-Symbols are used to show the physical state of the reactant or product.
s: solid l: liquid g: gas aq: aqueous
-Coefficients are used to balance equations.
-These are numbers placed in front of a formula.
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Balancing Equations
-All equations must be balanced because of the conservation of matter.
-All the atoms a reaction starts with it must end with.
Rules for balancing:
1. Write the correct formula for the reactants & products.
2. Count the number of atoms of each type on both sides.
3. Balance the elements one at a time adding coefficients in front of
the compound.
*Always have oxygen and hydrogen for last*
4. Check your work.
-Always place a coefficient in FRONT of a formula.
-NEVER place it in the middle of a formula.
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-NEVER change a subscript to balance an equation (only use coefficients.
-Changing a subscript changes the formula of the compound.
H2O is different than H2O2
-A one as a coefficient is understood. (Do not use “1’s”)
-In counting atoms for polyatomics, you multiply subscripts:
Fe(SO4)2
Fe: 1 atom
S: 2 atoms
O: 8 atoms
Balancing Equations
Examples:
__Al + __CuO ( __Al2O3 + __Cu
__C3H2 + __O2 ( __CO2 + _ H2O
__Al(OH)3 + __HBr (__ AlBr3 + __H2O
__Na3PO4 + __Fe2O3 (__Na2O + __FePO4
Balancing Equations
Practice:
___AgNO3 + __Cu ( __Cu(NO3)2 + __Ag
__C3H8 + __O2 ( __CO2 + _ H2O
__Mg + __N2 (__ Mg3N2
__Ag2SO4 + _AlCl3 (__AgCl + __Al2(SO4)3
Predicting Products
1. Combination
-Combine the two reactants into one product.
-When making the product, do not forget about writing formulas.
Examples
2Ca + O2 ( 2CaO
Mg + S ( MgS
6 K + N2 ( 2K3N
Special Case
-Metal oxides and water
MgO + H2O ( Mg(OH)2
2. Decomposition
-Decompose one reactant into two or more products.
Examples
NaCl ( Na + Cl
PbO2 ( Pb + O2
2 FeCl3 ( 2 Fe + 3 Cl2
Special Cases
-Metal carbonates
CaCO3 ( CaO + CO2
-Metal Chlorates
2 KClO3 ( 2 KCl +3 O2
-Metal nitrates
Ca(NO3)2 ( Ca(NO2)2 + O2
-Bases
Ca(OH)2 ( CaO + H2O
-Acids
HNO3 ( NO2 + H2O
3.Single Replacement
-Occurs only when one element is “more active” than another.
-A more active element will replace a less active element. (Use the activity series)
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Examples
3 Mg + 2AlCl3( 2 Al + 3 MgCl2
Zn + Li2SO4 ( 2 Li + ZnSO4
Br2 + MgCl2 ( NR
4.Double Replacement
-A metal replaces a metal & a nonmetal replaces a nonmetal in a compound.
-The reactants are ionic compounds in aqueous solution.
-Think about it like “foil” in algebra, first & last ions go together + inside ions go together.
AgNO3(aq) + NaCl(aq) ( NaNO3 + AgCl
Examples:
K2SO4 + Ba(NO3)2(
Na2CO3 + AgNO3(
CuCl2 + K2S(
Net Ionic Equations
Net Ionic Equations
-Equations shown so far are known as molecular equations.
-Molecular Equations: Shows complete the chemical formula of reactants & products.
-Since DR reactions involve aqueous solutions, the ionic compounds will break up into ions.
-You use the solubility rules to determine if the compound dissolves in water.
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Writing Equations:
AgNO3 + NaCl ( AgCl + NaNO3
-This is a molecular equation.
-Next split all the compounds into there ions, except any compound that is insoluble (forms a precipitate) according to the solubility rules.
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