Chapter 10
Chemical Reactions
3 types of formulas
• Molecular Formula: Identifies the actual
number of atoms in a molecule. e.g. H2O,
H2O2,
C6 H12 O6
• Empirical Formula: The simplest whole
number ratio of atoms in a compound. e.g.
H2O, HO, CH2O.
• Structural Formula: Shows the
arrangement of the atoms in the molecule,
bonds are shown.
3 types of formulas for Covalent
Compounds
• Molecular Formula: Identifies the actual
number of atoms in a molecule. e.g. H2O,
H2O2,
C6 H12 O6
• Empirical Formula: The simplest whole
number ratio of atoms in a compound. e.g.
H2O, HO, CH2O.
• Structural Formula: Shows the
arrangement of the atoms in the molecule,
bonds are shown.
Molecular and Formula Weights
• The sum of the atomic weights of all the atoms
in a chemical formula.
• The atomic weights are obtained from the
periodic table.
• For covalent compounds it is called molecular
weight, since the basic repeating unit is a
molecule. e.g. H2O, H2O2, C6 H12 O6
• For ionic compounds it is called formula weight,
since the basic repeating unit is a formula unit,
the simplest ratio of ions in an ionic compound.
e.g. NaCl, Ca(NO3)2.
Formula and molecular weights
Calculating Molecular and Formula Weights
• The molecular weight for C6 H12 O6 (glucose) is:
6C 6 x 12.01= 72.06 amu
12H 12 x 1.01= 12.12 amu
6O
6 x 16.00= 96.00 amu
Total 180.18 amu
• The formula weight for Ca(NO3)2 (calcium nitrate
is:
1 Ca 1 x 40.08 = 40.08 amu
2 N 2 x 14.01 = 28.02 amu
6O 6 x 16.00 = 96.00 amu
Total 164.10 amu
Calculating Molecular Weight
Chemical Reactions
• Occur when bonds are formed and broken.
• Involve changes in matter, creation of new
materials with new properties from existing
materials, energy changes.
• A chemical equation represents a chemical
reaction.
• Reactant(s)
Product(s)
• There can be one or more reactants and one or
more products.
• The arrow means “yield”.
The reaction occurring here is:
C + O2
CO2 + energy
Balancing Chemical Equations
• Combustion reaction:
C2H4 + O2
CO2 + H2O
Notice the numbers of oxygen, hydrogen, and
carbon atoms on each side are not the same. To
make them equal you can add a coefficient in
front of one or more of the chemical formulas:
C2H4 + 3O2
2CO2 + 2H2O
Now you have 2 carbon atoms, 4 hydrogen atoms,
and 6 oxygen atoms on each side of the
equation.
Chemical equations
In chemical
reactions,
subscripts don’t
change.
Reactants
Products
Arrow means yield and can be drawn both ways
Chemical equations
Only
coefficients
change.
Reactants
Products
Arrow means yield and can be drawn both ways
Rules for Balancing Equations:
• The same number of atoms of each element have to be
on each side of the equation. Atoms are neither created
nor destroyed in chemical reactions.
• Never alter the subscripts in the chemical formulas,
since those determine the identity of the chemical
compound. Only coefficients can be added.
• Leave the balancing of elements that appear by
themselves for last, since they are easier to manipulate.
• Balance polyatomic ions as an entity rather than as
individual atoms.
• Practice Sheet
Types of Reactions
• Combustion reactions occur when compounds
which contain C, H, and/or O, which are organic
compounds, react with oxygen (O2), to produce
carbon dioxide (CO2) and water vapor.
C6H12O6 + 9O2
6CO2 + 6H2O + energy
This is the reaction which occurs in the human and
animal body, respiration. This is the opposite of
photosynthesis.
Photosynthesis is:
6CO2 + 6 H2O + energy
C6H12O6 + 9O2
Products that contain substances that undergo combustion
Propane is combusted (burns). This heats up the air inside of the balloon.
Hot air is less dense than cold air and therefore it makes the balloon float.
Other examples of combustion
• C5H12 + 9O2
5CO2 + 6H2O + energy
This is the reaction for the combustion of octane, the
active ingredient in gasoline.
• C8H18 +
25
2
O2
• 2x(C8H18 +
25
2
8CO2 + 9H2O + energy
O2
• 2C8H18 + 25O2
8CO2 + 9H2O) + energy
16CO2 + 18H2O + energy
Combination Reactions
• Also called synthesis reactions
• X+Y
XY
• X and Y can be atoms or molecules, or
formula units.
e.g. 4Al + 3O2
2Al2O3
CO2 + H2O
H2CO3
Decomposition Reactions
• Opposite of combination reactions.
• XY
X+Y
Fe2O3
Fe + O2
K 2 CO3
K2O + CO2
Activity (Reactivity) of Metals and Hydrogen
Single Replacement Reactions
• XY + Z
ZY + X
• X and Z are metals or hydrogen.
• These reactions occur only if Z is more reactive than X.
• For instance, the alkali metals and alkaline earth metals can be “Z”
in the reaction and the transition metals or group IIIA or IVA metals
can be “X”, but not vice versa.
• Hydrogen is less reactive than Group IA, IIA, IIIA, and IVA metals,
but more reactive than some of the transition metals.
e.g. 2K + CuCl2
2KCl + Cu
2Ag + CaCl2
No reaction
Mg + 2H2O
2(H-OH)
H2 + Mg(OH)2
Reaction of Aluminum metal with copper (II) chloride (CuCl2)
2Al(s) + 3CuCl2(aq)
3Cu(s) + 2AlCl3(aq)
Double Replacement Reactions
• Also called ion exchange reactions.
• AX + BY
BX + AY
• A and B are metal ions, hydrogen, or ammonium ion
(positive ions). X and Y are nonmetal ions or polyatomic
ions (negative ions).
• Only occur if one of the products is a solid which is not
soluble in water, a liquid, or a gas.
e.g. CaCl2(aq) + Na2S(aq)
CaS(s) + 2NaCl(aq)
aq = aqueous (dissolved in water)
s = solid (not soluble in water) Also called a precipitate.
l = liquid
g = gas
Other examples of Double Replacement Reactions
Li2SO4(aq) + Mg(NO3)2(aq)
H3PO4(aq) + AlBr3(aq)
MgSO4 (s)+ 2LiNO3(aq)
AlPO4(s) + 3HBr(aq)
Also Double Replacement Reactions:
Neutralization Reactions are reactions of an acid (starts with H),
with a base (ionic compound ends in OH)
HCl(aq) + KOH(aq)
Acid
Base
KCl(aq) +
Salt
(Ionic compound)
2HNO3(aq) + Ca(OH)2(aq)
H2O(l)
(H-OH)
water
Ca(NO3)2(aq) + 2H2O(l)
2(H-OH)
The Law of Conservation of Mass
• The number of atoms of each element is the
same on either side of a chemical equation.
Therefore, if each atom is multiplied by its
atomic weight, the total weight is the same on
either side of a chemical equation.
• 2Na + O
Na2O
2 atoms Na
2 atoms Na
1 atom O
1 atom O
(2 x 22.99 amu) + (1 x 16.00 amu)
61.98 amu total
(2 x 22.99 amu) + (1 x 16.00 amu)
61.98 amu total
Law of Conservation of Mass
• H2 + O2
2H2O
• If 4g of hydrogen react with oxygen to
produce 36 g water, how many grams of
oxygen were needed?
• 2H2 + O2
2H2O
4g Xg
36g
• 4g + X g = 36 g Xg=32 g O2
The Mole
• Since atoms and molecules are tiny, a
grouping of atoms or molecules cannot be
a dozen or a crate or a carton.
• There is a special grouping used for atoms
and molecules which is called the mole,
abbreviated mol.
• 1 mol is equal to 6.02 x 1023 atoms,
molecules or formula units. This number is
called Avogadro’s number.
Molar Mass
• The mass of 1 mol of an atom, molecule or
a formula unit is equal to its formula mass
with the units of grams instead of amu.
• This is called the molar mass.
• Each mol consists of 6.02 x 1023 atoms or
molecules.
• The mass of 1 mol of NaCl, which has an
formula weight of 58.44 amu is 58.44 g.
• The mass of 1 mol of O2 is 32.00 g.
Exercises for Chapter 10
• p. 272-273 Applying Concepts:
# 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 16, 17.
p. 273-274 Parallel Exercises Group A:
# 1, 2, 4, 5, 6, 8, 9
New Book: p. 293-296 # 1, 2, 3, 4, 5, 6, 9, 10, 12,
13, 15, 16, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27,
30, 31, 32, 33, 34, 35, 36, 37, 39, 41, 42, 43, 45,
46, 47, 49, 50, 51, 52, 53.
p. 297-298 # 1, 2, 4, 5
Review
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Empirical, molecular and structural formulas.
Empirical and formula weights.
Balancing chemical equations.
Combustion reactions (organic compound with C, H, and/or O reacts
with oxygen to produce carbon dioxide and water)
Combination and decomposition reactions.
Single replacement reactions. The metal by itself must be more
reactive than the metal in the compound.
Double replacement reactions. The product must be a solid, a liquid,
or a gas.
Neutralization reactions. A special type of double replacement
reaction. An acid reacts with a base to produce a salt (ionic
compound) and water.
The law of conservation of mass.
Moles, molar mass and Avogadro’s number.