# Chemical Reactions

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```							 Chemical Reactions
1.   Signs of Chemical Change
2.   Conservation of Mass
3.   Organic Compounds
4.   Writing Equations
5.   Classifying Reactions
Signs of Chemical Change

Change in        Color Change
temperature
(energy)

Formation of      Formation of
precipitate       gas
Chemical Reactions
1.   Signs of Chemical Change
2.   Conservation of Mass
3.   Organic Compounds
4.   Writing Equations
5.   Classifying Reactions
Conservation of Mass
► Antoine   Lavoissier - Father of Chemistry

• developed rules of
quantitative chemistry
• measured the masses of all
reactants and products
• Law of Conservation of Mass
Law of Conservation of Mass

► What   goes in….must come out!
Balancing Equations
► Reactants  = substances combined that go
into the reaction
► Products = new substances formed that
come out of the reaction
Reactants  Products
Balancing Equations
► law of conservation of mass: mass of the
reactants must equal mass of the products
mass Reactants  mass Products

► We  now know that (#atoms)(atomic mass) = mass
► This means that:

#atoms Reactants  #atoms Products
Rules - Balancing Equations
1. Count the atoms of one element on both
sides of the equation
N2 + H2  NH3
2. Use coefficients (multiples) to increase
atoms of an element
N2 + 3H2  2NH3
3. NEVER change a formula (change/insert a
subscript)
N2 + H3  N2H3
Balancing Reactions
Al + O2    Al2O3
Balancing Equations - practice
1.     H2 +   O2 ---->    H2O

2.     Mg +   P4 --->    Mg3P2

3.     Cu +   O2 ---->    Cu2O
Balancing Equations - tips
► Lookfor polyatomic ions
► Count the ion as a unit

CaCl2 + AgNO3 ----> AgCl + Ca(NO3)2
Balancing Equations - tips
► Checkfor elements that occur more than
once on one side of an equation – sum the
atoms.

(NH4)2CO3 ---> NH3 + CO2 + H2O
Balancing Equations - tips
►    If you are balancing a combustion
reaction, balance in this order:
1.   Balance C
2.   Balance H
3.   Check if the coefficient in front of H2O is odd or even
4.   Double coefficients (except O2) if odd
5.   Balance O2

C2H6 + O2  CO2 + H2O

http://dbhs.wvusd.k12.ca.us/webdocs/Equations/Balance-Equation.html
Chemical Reactions
1.   Signs of Chemical Change
2.   Conservation of Mass
3.   Organic Compounds
4.   Writing Equations
5.   Classifying Reactions
Organic Compounds
► Organic   compound = a compound containing
carbon atoms
► Derived from living tissues
► ALL organic compounds must contain
carbon, but not all compounds that contain
carbon are organic!
Organic Compounds
► Carbon  atoms have     valence electrons.
►  carbon atoms must bond        times.
► The element that most commonly bonds to
carbon is hydrogen
Methane
► Methane  (CH4) : the simplest organic molecule
► Used for chemistry lab burners
Hydrocarbons
► Hydrocarbon = a molecule formed by a
chain of carbon atoms with hydrogen atoms
bonding to the chain
Alkanes
► Alkane  = generic name for all
hydrocarbons that have only single bonds
between atoms in the carbon chain
► The prefix “alk-” is changed to show how
many carbon atoms are in the chain
1 – meth       6 – hex
2 – eth        7 – hept
3 – prop       8 – oct
4 – but        9 – non
5 – pent       10 - dec
Alkanes
Name       Structural   Ball and Stick
Molecular    Formula       Model
Formula
Alkenes and Alkynes
► Alkene = has a
double bond in the
carbon chain

► Alkyne  = has a
triple bond in the
carbon chain
Determining Formulas
►   There are 2 methods for determining a
formula from a name:
1. Draw the molecule and count the carbons and
hydrogens
Draw propene:
2. Use the following formulas:
a)   Alkane: #H = 2(#C) + 2
b)   Alkene: #H = 2(#C)
c)   Alkyne: #H = 2(#C) - 2
Organic Nomenclature
Name     Molecular   Structural
Formula      Formula

C5H8

butane
Aromatics
► Aromatic:    is a “cyclic” hydrocarbon
► Cyclic hydrocarbons form ring structures
► Cycloalkanes have distinct odors
Aromatics
► Benzene:  an important cyclic hydrocarbon
used in industrial applications
Aromatics
Chemical Reactions
1.   Signs of Chemical Change
2.   Conservation of Mass
3.   Organic Compounds
4.   Writing Equations
5.   Classifying Reactions
Writing Equations
►    Equation: shorthand for writing a
chemical reaction (more formulas!)
►    Remember the 7 diatomic elements:
H,N,O,F,Br,Cl,I
►    Symbols:
1. Yields, forms, makes: ()
2. Solid (s) or precipitate (), liquid (l), gas (g)
or (), aqueous (aq)
Writing Equations
1.   Hydrogen and oxygen combine to yield
water.

2.   Calcium carbonate and hydrochloric acid
react to form water, carbon dioxide, and
calcium chloride.
Chemical Reactions
1.   Signs of Chemical Change
2.   Conservation of Mass
3.   Organic Compounds
4.   Writing Equations
5.   Classifying Reactions
Synthesis
► Synthesis  (combination): forming 1
substance from 2 or more substances
► General form:
A + B  AB
► Specific Example:
H2 + O2  H2O
*Key: look for one product
Decomposition
► Decomposition:  the breaking down of 1
substance into 2 or more substances
► General Form:
AB  A + B
► Specific Example:
CaCO3  CaO + CO2
*Key: Look for 1 reactant
Displacement Reactions
► Displacement   : one thing takes the place
of or pushes out another thing

Water displaced
by a rock
Single Displacement
► General   Form:
Ann-Tom + Crystal  Crystal-Tom + Ann
AT + C  A + CT
► Specific Example:
Zn + HCl  ZnCl2 + H2

   Single displacement: the replacement of 1 element
in a compound by another

*Key: Look for 1 element plus 1 compound on both
sides of the reaction
Single Displacement

► AgNO3   + Cu  ???
Double Displacement
► General    Form:
Ann-Bob + Crystal -Tom Crystal-Bob + Ann-Tom
AB + CT  CB + AT

► Specific   Example:
Na2O + FeCl3  Fe2O3 + NaCl

   Double displacement: the replacement of 1
element in a compound by another element from
a 2nd compound

*Key: Look for 2 compounds on both sides of the reaction
Double Replacement
1.   HCl + NaHCO3 

1.   PbNO3 + KI 
Activity Series
Activity Series
►   Activity series : a list in order of reactivity
of elements
►   Practice: determine if the following single
replacement reactions will occur
1) Pb + MgCO3 
2) Li + CuCl2 
3) Na + H2O 
Solubility
► Solubility = the ability of an ionic
compound to dissociate to its ions in water
► Ex: NaCl(s)  Na+(aq) + Cl-(aq)
Solubility
► Some   salts are soluble (above), some aren’t.

Strong bonds between the ions may
prevent them from dissociating.
Solubility Rules
Solubility Rules
Precipitation Reaction
►A  precipitate is a solid that forms out of
solution.
► A precipitation reaction is a double
displacement reaction that occurs
► NO reaction occurs if a precipitate does NOT
form
Precipitation Reaction
► Soluble NaCl + soluble
AgNO3 are reacted.
► AgCl and NaNO3 are the
possible products after
displacement
► the solubility rules are
used to determine that
AgCl is NOT soluble.
AgNO3(aq) + NaCl(aq)  NaNO3(aq) + AgCl(s)
Precipitation Reactions
►   Will the following double displacement
reactions occur?
►   If so, what is the formula for the
precipitate?

1) PbNO3 + NaCl 

2) Li2SO4 + NH4Br 
Predicting Products
► In order to predict the products of a
reaction, first classify the reaction.
► Use the Activity Series or the Solubility
Rules where applicable.
Chemical Reactions
1.   Signs of Chemical Change
2.   Conservation of Mass
3.   Organic Compounds
4.   Writing Equations
5.   Classifying Reactions
Review Reactions
1.   Signs of Chemical Change
2.   Writing Equations
3.   Balancing Equations
4.   Classifying Reactions
5.   Predicting Products
6.   Stoichiometry
Signs of Chemical Change
1.

2.

3.

4.
Writing Equations
1.   Writing   Molecular Formulas
2.   Writing   Ionic Formulas
3.   Writing   Organic Formulas
4.   Writing   Acid Formulas
Balancing Equations
► Use coefficients only
► Add all atoms of same element on one side
► Use subscripts for element AFTER it
► Use subscripts for all polyatomic ions in
parentheses
► Solve odd-even problems by doubling all
coefficients
Balancing Equations
1.   N2 + H2      NH3

2.   C2H6 + O2     CO2 +   H2O

3.   P4 + O2      P2O5
Classifying Reactions
1.   Synthesis: 1 product
2.   Decomposition: 1 reactant
3.   Single Replacement: element +
compound
4.   Double Replacement: compound +
compound
5.   Combustion: hydrocarbon + O2  CO2 +
H2O
Predicting Products
► Classify   reaction and finish based on type of
reaction
► Use the reference package for help!!
► Use Activity Series for SR reactions
► Use Solubility Rules for DR reactions
Stoichiometry
► Mol-mol  problems: 1 step
- this is the ONLY step that can be used
to switch from one substance to another!
► Mol-mass problems: 2 steps
► Mass-mass problems: 3 steps
► 2 givens: 2 problems
- limiting reagent: reactant that makes
less product
- % yield = actual/theoretical
= lab/calculated

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