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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