Download Chemical Reactions.

Chemical Reactions.
Vocabulary:
Define each word and use it in a sentence or
create a diagram/illustration
Compound
Chemical formula
3.  Subscript*
4.  Coefficient
1. 
2. 
CO2 emissions
Fossil fuels:
C8H18(l) + O2(g) à CO2(g) + H2O(g)
Liquid gasoline reacts with oxygen to
produce carbon dioxide and water
Ocean Acidification:
CO2(g) + H2O(l) à H2CO3(aq)
Carbon dioxide dissolves in water to produce
carbonic acid.
Anatomy of a chemical formula
chemical formula: a combination of symbols and
numbers that describe the amount and type of atoms
that form a compound.
Example:
CuSO4(aq)
Atomic symbols describe the type of atoms in the
compound
(copper→ Cu, sulfur→ S, oxygen→ O)
subscript numbers appear after the atomic symbol
and describe the number of atoms in the compound
(1 copper, 1 sulfur, 4 oxygen)
subscript letters describe the physical state of the
compound: s = solid, l = liquid, g = gas, aq = aqueous!
study question 1
H2CO3(aq)
1. 
2. 
3. 
4. 
In the above formula:
How many H atoms?
How many C atoms?
How many O atoms?
What is the physical state?
Describing Chemical Reactions
An equation describes a chemical reaction or
a physical change
n  Reactants: chemicals that react
n  Products: chemicals that are formed
n  e.x. sodium + oxygen à sodium oxide
Na(s) + O2(g) à Na2O(s)
reactants
product
study question 2
1. 
2. 
Write the chemical equation for carbon (C)
reacting with oxygen (O2) to form carbon dioxide
(CO2)
Label the reactants and products
Balancing Chemical Equations
The Law of Conservation of Matter: Matter
cannot be created or destroyed.
n  For chemical equations: The total number of
each type of atom must be the same before
and after the reaction
example
n 
Sodium (Na) reacts with oxygen (O2) to
produce sodium oxide (Na2O)
Na(s) + O2(g)➜Na2O(s)
How many sodium (Na) atoms react?
n  How many sodium (Na) atoms are in the
product?
n  This violates the law of conservation of
matter!
n 
study question 3
C8H18(l) + O2(g) à CO2(g) + H2O(g)
Count the number of
Count the number of
atoms on the reactants atoms on the products
side
side
C ____
C ____
H ____
H ____
O ____
O ____
Does this equation obey the law of
conservation of matter?
Example:
4 Na(s) + O2(g) à 2 Na2O(s)
SUBSCRIPTS CAN NOT CHANGE!
You may NEVER change a formula
n 
Coefficients are used to balance the equation
n  These apply to the entire formula (all the
atoms)
n 
n 
4Na = 4 sodium atoms
2Na2O = 4 sodium (Na) atoms and 2 oxygen(O)
atoms
study question 4
CO2(g) + H2O(l) à H2CO3(aq)
Count the number of
Count the number of
atoms on the reactants atoms on the reactants
side
side
Carbon (C) ____
Carbon (C) ____
Oxygen (O) ____
Oxygen (O) ____
Hydrogen (H) ____
Hydrogen (H) ____
Does this equation obey the law of
conservation of matter?
Rules of Balancing Equations
Write the equation using
correct formulas. You may
NOT change the formula in any
way.
2.  Balance the equation using
coefficients
1. 
Balancing example:
sodium and oxygen react to form sodium oxide
Na + O2 à Na2O
Take atomic inventory: (you must obey the Law
of Conservation of Matter)
Reactants:
Products:
Na
O
Na
O
1
1
2
2
Problem: begin with 2 oxygen atoms(O) but end with
only 1
This breaks the law of conservation of matter.
Na + O2 à 2Na2O
(= Na2O + Na2O)
solution: Add the coefficient ‘2’ in front of Na2O
Take atomic inventory again:
Reactants:
Na
O
1
2
Products:
Na
O
4
2
Problem: begin with 1 sodium atom(Na) but end with
4. This breaks the law of conservation of matter.
4 Na + O2 à 2Na2O
solution: Add the coefficient ‘4’ in front of Na
Take atomic inventory again:
Reactants:
Na
O
4
2
Products:
Na
O
4
2
4 sodium atoms combine with 1 oxygen molecule to
form 2 formula units of sodium oxide. This equation
obeys the Law of Conservation of Matter.
study question 5
n 
1. 
2. 
3. 
BALANCE THE FOLLOWING REACTIONS:
H2(g) + O2(g) à H2O(l)
Na2CO3(s) + HCl(aq) à NaCl(aq) + CO2(g) + H2O(l)
K2SO4(aq) + CaCl2(aq) à CaSO4(s) + KCl(l)
Types of Chemical Reactions.
1. Combination.
n  Also
called synthesis
n  Two or more reactants combine to
form one product
n  e.x. 2 Na(s) + Cl2(g) à 2 NaCl(s)
n  A + B à AB
study question 6
Which equation represents a synthesis
reaction?
n 
2Ca(s) + O2(g) à 2CaO(s)
n 
2KClO3(s) à 2KCl(s) + O2(g)
2. Decomposition.
n  One
reactant decomposes to form
two or more products.
n  2H2O(l) à 2H2(g) + O2(g)
n  AB à A + B
study question 7
Which equation represents a decomposition
reaction?
n 
2Ca(s) + O2(g) à 2CaO(s)
n 
2KClO3(s) à 2KCl(s) + 3O2(g)
3. Single Replacement.
n  An
atom replaces an ion in a compound.
n  Mg(s)
+ CuSO4(aq) à MgSO4(aq) + Cu(s)
n  Cl2(g)
+ 2KI(aq) à I2(s) + 2KCl(aq)
n  A
+ BC à AC + B
study question 8
Which equation represents a single replacement
reaction?
•  2NaI(s) + Cl2(g) à 2NaCl(s) + I2(s)
•  2NaI(aq) + Pb(NO3)2(aq) à 2NaNO3(aq) + PbI2(s)
4. Double Replacement.
n  Ions
n  Ca
from different compounds switch
places.
CO3(s) + 2HCl(aq) à CaCl2(s) + H2 CO3(aq)
n  AB
+ CD à AD + CB
study question 9
Which equation represents a double replacement
reaction?
•  2NaI(s) + Cl2(g) à 2NaCl(s) + I2(s)
•  2NaI(aq) + Pb(NO3)2(aq) à 2NaNO3(aq) + PbI2(s)
5. Combustion reactions.
n 
n 
n 
n 
A compound reacts with oxygen (O2)
often produces CO2 & H2O
e.x. C3H8(g) + 5O2(g) à 3CO2(g) + 4H2O(g)
Note: a combustion reaction can also be a
decomposition or a combination reaction
Study question 10
n 
Write the combustion reaction for gasoline:
C8H18(l)