Download Chemical Change and Reaction Types

YEAR 10 CHEMISTRY
Chemical Reactions
Physical & Chemical Changes
What is the difference between a physical
and a chemical change?
 A physical change is one in which no new
substance is formed eg ice melting
 A chemical change or chemical reaction
has occurred if one or more new
substances are formed.
3
PHYSICAL
Changes shape
Breaks into smaller
pieces
Dissolves
Mixed with another
substance
Changes state
No new substances
formed
CHEMICAL
A permanent colour
change
A gas is given off
Change in
temperature
Precipitate forms
One metal is
deposited on another
New substances are
formed
Evidence of chemical changes
1. Colour change
5
2. A gas is given off
6
3. Temperature changes

Endothermic reactions - absorb heat and
as a result the temperature falls
Demo

Exothermic reactions - release heat and
as a result the temperature rises
Demo
7
Endothermic reaction



Endothermic reaction
of barium hydroxide
and an ammonium
salt.
Mix the two solids;
they react, and the
products dissolve in
water of hydration.
The reaction feels
cold.
8
Exothermic reaction

Contains sodium
acetate
9
Metal deposition

Sometimes one metal can coat another
metal. An example is an iron nail placed
in a solution of copper sulfate. The result
is an orange coating on the nail. The
coating is copper metal.
Precipitation

When two solutions are mixed, sometimes
a solid is formed. The solid is called a
precipitate.
Chemical Reactions
Types of Chemical Reactions
There are five types of chemical reactions we will talk about:
1.
2.
3.
4.
5.
Synthesis: A + B -> AB
Decomposition: AB -> A + B
Precipitation: a solid forms
Combustion: uses oxygen
Single Displacement: A + BC -> AC + B
Double Displacement: AB + CD -> AD + CB
You need to be able to identify the type of reaction and predict the product(s)
13
1. SYNTHESIS
•
Synthesis reactions occur when two substances
(generally elements) combine and form a compound.
•
Sometimes called combination or addition reactions.
•
In general: A + B  AB
reactant + reactant  1 product
•
Example:
C + O2  CO2
1. SYNTHESIS

Hydrogen and oxygen yields water
2H2 + O2  2H2O

Magnesium plus nitrogen yields magnesium nitride
3Mg + N2  Mg3N2

Iron and sulfur yields iron(II) sulfide
Fe + S  FeS
15
Practice
Predict the products. Write and balance the following
synthesis reaction equations.
•
Sodium metal reacts with chlorine gas
Na(s) + Cl2(g) 
•
Solid Magnesium reacts with fluorine gas
Mg(s) + F2(g) 
•
Aluminum metal reacts with fluorine gas
Al(s) + F2(g) 
2. DECOMPOSITION
•
Decomposition reactions occur when a compound
breaks up into the elements or in a few to simpler
compounds
•
In general: AB  A + B
1 Reactant  Product + Product
•
Examples:
2H2O  2H2 + O2
2HgO  2Hg + O2
2.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: 2Al(ClO3)3  2 AlCl3 + 9 O2
•
There are other special cases, but we will not explore these
Practice
Predict the products. Then, write and balance the following
decomposition reaction equations:
•
Solid Lead (IV) oxide decomposes
PbO2(s) 
•
Aluminum nitride decomposes
AlN(s) 
Practice
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) 
•
NH3(g) + H2CO3(aq) 
3. PRECIPITATION

Two solutions mixed together make a solid
AgNO3 (aq) + NaCl (aq)
2 clear
solutions
reacting to
form a
yellow
precipitate
AgCl (s) + NaNO3 (aq)
AgCl
precipitate
21
4. COMBUSTION

Uses oxygen, happens quickly and
produces heat and light.
22
Hydrocarbon combustion reactions
What do you notice about these
combustion reactions?
 Balance:

23
5. NEUTRALISATION
Acid + base reaction
 Produces salt and water.
 Example:

HCl(aq) + NaOH(aq)
NaCl (aq) + H2O (l)
24
6. DISPLACEMENT
One metal deposits on another. A metal
solution reacts to become the pure solid
metal.
 Example:
Zn(s) + CuSO4(aq)
ZnSO4(aq) + Cu(s)

Amanda Clarke 2007
6. Single Displacement
Fe(s) + CuSO4(aq)
FeSO4(aq) + Cu(s)
Example: When an iron nail placed
in a solution of copper sulfate the
result is an orange coating on the
nail. The coating is copper metal.
Classify the following reactions:
C3H8(l) + 5O2
Combustion
 HNO3(aq) + LiOH(aq)
Neutralisation
 CuSO4 + 2NaOH(aq)
Precipitation
 2Na(s) + Cu(NO3)2
Displacement
 KMnO4(s)
Decomposition
 N2(g) + O2(g)
Combination

3CO2(g) + 4H2O(l)
LiNO3 (aq) + H2O (l)
Na2SO4(aq) + Cu(OH)2(s)
2NaNO3 (aq) + Cu(s)
KMnO2(s) + O2(g)
2NO(g)
27
Symbols used in Chemical
reactions

(s) solid

(l) liquid

(g) gas

(aq) aqueous (a solution: means the
substance is dissolved in water)
Amanda Clarke 2007
Classify the following reactions:
C3H8(l) + 5O2
Combustion
 HNO3(aq) + LiOH(aq)
Neutralisation
 CuSO4 + 2NaOH(aq)
Precipitation
 2Na(s) + Cu(NO3)2
Displacement
 KMnO4(s)
Decomposition
 N2(g) + O2(g)
Combination

3CO2(g) + 4H2O(l)
LiNO3 (aq) + H2O (l)
Na2SO4(aq) + Cu(OH)2(s)
2NaNO3 (aq) + Cu(s)
KMnO2(s) + O2(g)
2NO(g)
Amanda Clarke 2007
Reactants and products



Write an equation that
shows this experiment.
Indicate the reactants
Indicate the products
30
Word and chemical equations
Word equation
Hydrogen + oxygen
Chemical equation
2H2 + O2
water
2H2O
31
Symbols used in
Chemical equations
(s) solid
 (l) liquid
 (g) gas
 (aq) aqueous - the substance is dissolved
in water (solution)
  a gas is given off
 ↓ a precipitate forms (a solid in a solution)

32
When balancing an equation focus on just
ONE element at a time.
 Don't try and do it all in your head.
 Choose an element, balance it and then in
the next step worry about how your
attempt at balancing has effected other
elements.

33
Balancing chemical equations
Na + H2O
NaOH + H2
 This 'equation' is NOT balanced!
 Only place numbers at the front.

34