Types of Chemical Reactions
& Counting Atoms
Grade 10 Chemistry
Recall
Reactant + reactant  product
Word equation
Sodium + chlorine  Sodium chloride

Chemical equation
Na + Cl  NaCl

Types of Reactions
Synthesis
 Decomposition
 Single-displacement
 Double-displacement
 Combustion

Synthesis Reactions
Two substances (elements) combine
and form a compound
A+BC

– Reactant + reactant  product
– Carbon + oxygen  Carbon dioxide
– C + O2  CO2
Decomposition Reactions
Compound breaks down into two
elements (or simpler compounds)
 Reverse of synthesis
CA+B

– Reactant  product + product
– Water  hydrogen + oxygen
– 2 H2O  2H2 + O2
Single-displacement Reactions

One element replaces another element in a
compound
– Metal replaces a metal
– Non-metal replaces a non-metal

Get a new element and a different compound
 A + BC  AC + B
– zinc + hydrochloric acid  zinc chloride + hydrogen
Double-displacement Reactions

Ions from two compounds change places
– Metal replaces a metal
– Non-metal replaces a non-metal

AB+ CD  AD + CB
– Sodium chloride + silver fluoride Sodium fluoride
+ silver chloride
Combustion Reactions
A substance reacts with oxygen to
produce carbon dioxide and water
 X + O2  CO2 + H2O

Reactivity

Reactive - will readily take part in
chemical reactions
Reactivity
A more reactive element can displace a
less reactive element in a single
displacement reaction
 Applies to Alkali metals (Group 1)

Reactivity Series
Reactivity Example
Single displacement reaction:
 Copper is more reactive than silver


Cu + AgNO3  CuNO3 + Ag

The copper displaces the silver in the
compound silver nitrate
Reactivity Example Continued
Single displacement reaction:
 Silver is less reactive than copper


Ag + CuNO3  AgNO3 + Cu

The silver cannot displace the copper
because it is less reactive. Chemical
reaction does not occur
Counting Atoms
RULES FOR COUNTING ATOMS
1.
SUBSCRIPTS only refer to the
atom that they are BEHIND. For
example…
H2S
There are TWO atoms of
HYDROGEN and only ONE atom
of SULFUR.
COEFFICIENTS
2.
COEFFICIENTS apply to the entire
compound. You MULTIPLY the
coefficients and SUBSCRIPTS.
2 H2S
ATOMS OF HYDROGEN: 4
ATOMS OF SULFUR: 2
IF THERE ISN’T A SUBSCRIPT BEHIND AN
ELEMENT, ASSUME THERE IS ONLY ONE ATOM OF
THAT ELEMENT!
PARENTHESES
3. If elements or compounds are inside of
PARENTHESES, then the SUBSCRIPT
behind the parentheses applies to
everything inside the parentheses.
Ba(OH)2
ATOMS OF BARIUM:
1
ATOMS OF OXYGEN:
2
ATOMS OF HYDROGEN: 2
LET’S PRACTICE!
MgCl2
Atoms of Magnesium: 1
Atoms of Chlorine: 2
Al2S3
Atoms of Aluminum: 2
Atoms of Sulfur: 3
PRACTICE
H2SO4
Atoms of Hydrogen: 2
Atoms of Sulfur:
1
Atoms of Oxygen:
4
Atoms of Carbon:
Atoms of Hydrogen:
Atoms of Oxygen:
CH3OH
1
4
1
THIS COULD BE A LITTLE
TRICKY…
Ca3(PO4)2
Atoms of Calcium: 3
Atoms of Phosphorus: 2
Atoms of Oxygen: 8
Al2(SO4)3
Atoms of Aluminum: 2
Atoms of Sulfur: 3
Atoms of Oxygen: 12
Homework
Counting atoms worksheet
 Predict products of worksheet
