Download Chemical Reactions – Chapter 9 _- the process by which the atoms

Chemical Reactions – Chapter 9
What is a chemical
reaction?
List the four things
that are evidence
of a chemical
reaction in the
demo shown in
class.
_____________________________- the process by which the atoms of one or more substances are
rearranged to form different substances.
Evidence of a Chemical Reaction
1.
Release of a __________
2.
Color changes
3.
Formation of a ____________________
a.
A precipitate is a solid product formed by the reaction of two aqueous solutions.
b.
It is abbreviated _________
4.
Changes in heat and light
a. All reactions either absorb or release _________________
Writing Chemical
Equations:
__Reactants___  __Products___
• Reactants—the _____________________ substance(s).
• Products—the substance(s) _____________________ during the reaction.
Example:
•
+, , (s), (l), (g), (aq), , N.R., , catalyst
•
 & catalyst are written above the yield sign
Examples: What is the arrow pointing to?
H2 (g) + O2 (g)  H2O (g)
H2O2 (aq) →
Why might you add
heat to reactants in
a chemical
equation?
_____________
CaCO3
→
_________
___________
H2O (l) + O2 (g)
_____________
CaO (s) + CO2 (g)
USE PENCIL!!
________
Writing and
Balancing
Chemical
Equations
_______________
Conservation of Mass
• Because of the principle of the _____________________________ of mass, an equation must be
balanced. It must have the same number of atoms of the same kind on
______________________________.
Example:
Write the equation for the formation of sodium hydroxide and hydrogen, from the
reaction of sodium with water.
1. Write the formulas of all reactants to the left of the arrow and all products to the right of
the arrow.
___________ + ___________ →
_______________ + ________________
Translate the equation and be sure the formulas are correct.
___________ + ___________ →
_______________ + ________________
2. Once the formulas are correctly written, DO NOT change them.
• Use coefficients (numbers in front of the formulas), to balance the equation.
• DO NOT CHANGE THE SUBSCRIPTS!
• Coefficients are always __________________ numbers.
• The subscripts tell you how many of a particular element are in a compound.
• The coefficient tells you about the _____________________, or number, of molecules or
formula units of the compound.
_____Na + _____H2O  ____NaOH + _____H2
Writing and Balancing Chemical Equations
3. Begin balancing with an element that occurs only once on each side of the arrow.
Ex: Na
__2___Na + ___2__H2O  __2__NaOH + _____H2
When you are finished, you should have equal numbers of each element on either side
of the equation
Na
____
Na
____
H
____
H
____
O
____
O
____
4. To determine the number of atoms of a given element in one term of the equation,
multiply the coefficient by the subscript of the element
Ex: In the previous equation (below), how many hydrogen atoms are there?
__2___Na + ___2__H2O  __2__NaOH + _____H2
There are ________________________
Helpful Hints:
•
Take one element at a time, working left to right except for H and O. Save H for nextto-last, and O until last.
•
IF everything balances except for O, and there is no way to balance O with a whole
number, double all the coefficients and try again. (Because O is diatomic as an element)
(Shortcut) Polyatomic ions that appear on both sides of the equation should be
balanced as independent units.
•
Practice:
Balance the chemical equation:
___ Al(s) + ___ Br2(l) ---> ___ Al2Br6(s)
Balance the equation for the formation of magnesium nitride from its elements.
Balance the reaction of sodium metal with chlorine gas to form sodium chloride
Coefficients are always whole numbers:
Ex:
_____NH3 + _____O2  _____NO2 + ____H2O
•
H can be balanced by placing a 2 in front of NH3 and a 3 in front of H2O. Then put a 2 in
front of NO2 for nitrogen to balance.
Now all that is left to balance is the oxygen. There are 2 O on the reactant side and 7 on
•
the product side. Our only source of oxygen is the O2. Any whole number we place in
front of the O2 will result in an even number of atoms. The only way to balance the
equation is double all the coefficients.
Double all the coefficients, then add the 7 for the O2.
•
Practice
____H2 + ____O2  ____H2O
equations:
___NH3 + ____O2  ____NO2 + ____H2O
___Ca + ___H2O  ___Ca(OH)2 + ___H2
__NH4Cl + __Ca(OH)2  __NH3 + __H2O + __CaCl2
___ZnO + ___HCl  ___ZnCl2 + ___H2O
____K + _____F2  _____KF
____C2H4 + ____O2  ____CO2 + ____H2O
Synthesis
reaction/
combination
reaction
EXAMPLES:
• the combination of two or more substances to form a compound
Element or compound + element or compound  compound
General form A + B  AB
• The product in a reaction will have different properties from either of the reactants that
formed it.
Predict the products. Write and balance the following synthesis reaction equations.
Sodium metal reacts with chlorine gas
Solid Magnesium reacts with fluorine gas
Aluminum metal reacts with fluorine gas
Decomposition
Reaction:
•
•
•
is the breakdown of one substance into two or more other substances
compound  two or more elements
AB  A + B
Decomposition Exceptions
• Carbonates and chlorates are special case decomposition reactions that do not go to the
elements.
• Carbonates (CO32-) decompose to carbon dioxide and a metal oxide
• Example: CaCO3  CO2 + CaO
• Chlorates (ClO3-) decompose to oxygen gas and a metal chloride
• Example: 2 Al(ClO3)3  2 AlCl3 + 9 O2
EXAMPLES:
Predict the products. Then, write and balance the following decomposition rxn equations:
Solid Lead (IV) oxide decomposes
Aluminum nitride decomposes
Practice
equations:
Identify the type of reaction for each of the following synthesis or decomposition reactions,
and write the balanced equation:
N2(g) + O2(g) 
BaCO3(s) 
Co(s)+
S(s) 
NI3(s) 
Single
Replacement
Reaction:
EXAMPLES:
•
One element replaces another element in a compound.
element + compound  element + compound
A
+ BC
 AC
+
B
When H2O splits into ions, it splits into H+ and OH- (not H+ and O-2 !!)
Write and balance the following single replacement reaction equation:
Zinc metal reacts with aqueous hydrochloric acid
Sodium chloride solid reacts with fluorine gas
Aluminum metal reacts with aqueous copper (II) nitrate
To determine if a single replacement reaction will take place, you must compare the activities
of the elements involved.
Activity Series of
•
For metals, use the Activity Series. A __________ will
Nonmetals
Decreasing
Activity
replace any metal below it on the activity series.
___I2 + ___NaCl 
Fluorine
Chlorine
Bromine
Iodine
___AgNO3 + ___Mg 
___KBr + ___F2 
___Mg(NO3)2 + ____Cu 
Double
Replacement
Reaction:
Two elements replace each other in compounds.
• occur when a metal replaces a metal in a compound and a nonmetal replaces a nonmetal
in a compound
AB + CD  AD + CB
• 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)
•
In order for double replacement reaction to take place, one of the products must be
an insoluble solid (ppt), a gas, water.
Would this
compound be a
precipitate?
•
•
•
BaSO4
Ag2S
NH4Cl
_______
_______
_______
Pb(NO3)2
PbCl2
Cr PO4
_______
_______
_______
__Na2SO4 + __Ba(NO3)2 
EXAMPLES:
__NaOH + __Fe(NO3)3 
Predict the products. Balance the equation
Practice
HCl(aq) +
AgNO3(aq) 
equations:
CaCl2(aq) +
Na3PO4(aq) 
Pb(NO3)2(aq) +
FeCl3(aq) +
NaOH(aq) 
H2SO4(aq) +
NaOH(aq) 
KOH(aq) +
Combustion
Reactions:
BaCl2(aq) 
•
•
CuSO4(aq) 
occur when a hydrocarbon reacts with oxygen gas.
This is also called burning!!! In order to burn something you need the 3 things in the “fire
triangle”:
1. A Fuel (hydrocarbon)
2. Oxygen to burn it with
3. Something to ignite the reaction (spark)
General form for combustion of a hydrocarbon:
CxHy + O2  CO2 + H2O
• Products in combustion are ALWAYS _________________________________ and ___________________.
(although incomplete burning does cause some by-products like carbon monoxide)
Example:
C5H12 +
O2 
CO2 +
H2O
EXAMPLES:
Write the products and balance the following combustion reaction:
C10H22 + O2 
____C3H8 + ____O2  ____CO2 + ____H2O
____C6H12O6 + ____O2  ____CO2 + ____H2O
Practice
State the type, predict the products, and balance the following reactions:
equations:
BaCl2 +
H2SO4 
C6H12 +
O2 
Zn +
CuSO4 
Cs +
Br2 
FeCO3 