UNIT VI
Types of Chemical Reactions
Lesson 2
VI.5 TYPES OF CHEMICAL
REACTIONS


When we classify reactions by how atoms are
rearranged, there are 5 MAJOR TYPES of
reactions:
http://www.youtube.com/watch?v=i-HHvx1VC_8
VI.5 TYPES OF CHEMICAL
REACTIONS
1. Synthesis - is the combination of two or more
substances to form a _____________________________.
A + B → AB
Examples:
2H2 (g) + O2(g) → 2H2O (g)
CaO(s) + H2O(l) → Ca(OH)2 (s)
2Fe(s) + O2(g) → 2FeO(s)


How to predict the products: assume product is made
of the two reactants joined together.
http://www.youtube.com/watch?v=A5H6DVe5FAI&feature
=related
VI.5 TYPES OF CHEMICAL
REACTIONS
2. Decomposition – is the opposite of synthesis; one
substance breaks down to form two or more
________________________________.
AB → A + B
Examples:
CO2 (g) → C(s) + O2(g)
2Ag2O(s) → 4Ag(s) + O2(g)


How to predict the products: the products will be the
elements that make up the original compound.
http://www.youtube.com/watch?v=ezsur0L0L1c&feature=re
lated
VI.5 TYPES OF CHEMICAL
REACTIONS
3. Single Replacement – occurs when one element is replaced by
another element in a compound.
A + BC→ AC + B
Examples:
Cl2 (aq) + 2KBr(aq) → 2KCl(aq) + Br2 (aq)
Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
*This is when an ELEMENT reacts with a compound and
REPLACES an element in the compound.
 How to predict the products: replace metal with metal OR replace
nonmetal with nonmetal.
CuI2 + Fe → FeI2 + Cu
(Cu is replaced by Fe – METAL)
CuI2 + Br2 → CuBr2 + I2
( I is replaced by Br – NONMETAL)
http://www.youtube.com/watch?v=hKtynbVtMKc&feature=related
VI.5 TYPES OF CHEMICAL
REACTIONS
4. Double Replacement – occurs when the elements in a
solution of reacting compounds ______________ places, or
________________ each other.
AB + XY→ AY + XB
Examples:
ZnBr2(aq) + 2AgNO3(aq) → 2AgBr(s) + Zn(NO3)2 (aq)


*This is when TWO COMPOUNDS react – pay close
attention to CHARGE on ions.
http://www.youtube.com/watch?v=opY3FLrPTa4
VI.5 TYPES OF CHEMICAL
REACTIONS
4. Double Replacement
AB + XY→ AY + XB
ZnBr2(aq) + 2AgNO3(aq) → Zn(NO3)2 (aq) + 2AgBr(s)
Note that compounds are made of ions put together. What you
will do is take a positive ion on the reactant side and
exchange it with the positive ion on the product side.
BE VERY careful about the charges and how you combine the
ions together to make a new compound.
http://www.youtube.com/watch?v=opY3FLrPTa4
VI.5 TYPES OF CHEMICAL
REACTIONS



A special type of double replacement reaction...
Neutralization – reaction between an ACID and a
BASE (the H in the acid and the OH in the base form
H2O)
the products are always WATER and SALT
Acid + Base → Salt + Water
HB + XOH → XB + HOH
Examples:
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
VI.5 TYPES OF CHEMICAL
REACTIONS

A special type of double replacement reaction...
Neutralization
Example:

VI.5 TYPES OF CHEMICAL
REACTIONS
5. Combustion – chemical reaction that usually gives off a
large amount of energy in the form of heat or light
 involves the reaction of a substance with OXYGEN (O2)
 hydrocarbons (compounds made of H and C) are involved
 carbon dioxide and water are produced
CxHy + O2 → CO2 + H2O
Ex:

C3H8(g) + 5O2(g) →
3CO2(g) + 4H2O(g)
http://www.youtube.com/watch?v=UygUcMkRy_c
VI.5 TYPES OF CHEMICAL REACTIONS
5. Combustion ---Special notes
CxHy + O2 → CO2 + H2O
If you have an organic compound with O, you get the same
thing
+ O2 → CO2 + H2O
If you have an organic compound with S, you get:
Sulphur dioxide reacts with water to form sulphurous
acid(acid rain)
-----Nice SUMMARY on p. 118 of your Hebden textbook-----
VI.5 TYPES OF CHEMICAL
REACTIONS
Predicting Products
1. Synthesis (2 elements form one compound)
Mg + I2 →
2. Decomposition (1 compound breaks into
elements)
HgO →
VI.5 TYPES OF CHEMICAL
REACTIONS
Predicting Products
3. Single Replacement (interchange metal or nonmetal)
Mg +
AlCl3 →
4. Double Replacement (interchange positive ions
in compound)
FeCl2 + K2S
→
VI.5 TYPES OF CHEMICAL
REACTIONS
Predicting Products
5. Combustion (products will be carbon dioxide and
water)
C6H14 +
O2
→
VI.6 ENERGY CHANGES IN
CHEMICAL REACTIONS

In a chemical reaction, BONDS are broken and
new bonds are formed. ENERGY is required to
break these bonds.
Endothermic Reactions
 ABSORB heat (energy) from the surroundings
Ex:
HCl + energy → H + Cl
 energy appears on the REACTANT side
 there is more energy at the end of the reaction
(as reaction proceeds, more energy is required to
break the bonds)
VI.6 ENERGY CHANGES IN
CHEMICAL REACTIONS
Endothermic Reactions
VI.6 ENERGY CHANGES IN
CHEMICAL REACTIONS
Exothermic Reactions
 GIVES OFF heat (energy) to the surroundings
Ex:
H + Cl → HCl + energy
energy appears on the PRODUCT side
 there is more energy at the beginning of
reaction (as reaction proceeds, energy is lost to
the surroundings)

VI.6 ENERGY CHANGES IN
CHEMICAL REACTIONS
Exothermic Reactions
VI.6 ENERGY CHANGES IN
CHEMICAL REACTIONS

∆H = change in enthalpy (the heat contained in
the system)
Endothermic Rxn: ∆H is positive
Ex:
A + 45kJ → B
A → B
∆H = + 45kJ
VI.6 ENERGY CHANGES IN
CHEMICAL REACTIONS
Exothermic Rxn:
Ex:
∆H is negative
C → D + 65kJ
C → D
∆H = - 65kJ
Summary: HEAT on LEFT -----> ∆H = +ve
HEAT on RIGHT -----> ∆H = -ve
VI.6 ENERGY CHANGES IN
CHEMICAL REACTIONS

∆H of the products and reactants:
LET US TRY (INTRO TO UNIT 7 )

C12H22O11 + 12O2  12CO2 + 11H2O + 5638 kJ

How much heat is released during the formation of 9.6
moles of CO2?
HOMEWORK
Balancing & Types of rxns:
Questions: p. 118 # 65 -66 (every 3rd), 67 (every 2nd one)

Endo vs Exo
 Questions: p. 120 #68 - 80