CHEMICAL
REACTIONS
Chemical Reactions
Chemical change = Chemical reaction
Substance(s) is used up (disappear)
New substance(s) is formed.
What is a chemical reaction?
A chemical reaction is a change that takes
place when one or more substances
(called reactants) form one or more new
substances (called products).
Main Ideas
Chemical Reactions are represented by
Chemical Equations.
Chemical Equations are balanced to show the
same number of atoms of each element on
each side.
The Law of Conservation of Mass says that
atoms won’t be created or destroyed in a
chemical reaction. That is why you have to
balance chemical equations!
How can you spot a chemical
reaction?
Chemical reactions can appear very different.
As you observe a chemical reaction, you may
detect:
a colour change
precipitate (solid) forming
energy being produced (fizzing, burning)
an odour being produced.
evolution of gas (formation of bubbles)
Signs/Demo of Chemical
Reactions
How do you know when a
chemical reaction takes place?
Temperature Change
Change in Acidity
Representing Chemical Reactions
Chemists observe chemical reactions and
have come up with a way to represent or
model what is happening.
Making NaCl
Solid Sodium combines with Chlorine gas
to make solid Sodium Chloride:
2Na (s) + Cl2 (g)
2NaCl
Chemical Equations are different from
Numerical Equations
Numerical Equation: 3x + 2y = 47
Chemical Equation 2Na + Cl2 2NaCl
ReactantA + Reactant B
Product
The reactants are used up in forming the
product
The arrow
shows the direction of the
reaction
What is a word equation?
What is a symbol equation?
Meaning of Chemical Formula
Symbols used in Chemical Equations
Law of Conservation of Mass
In a chemical reaction, matter is neither
created nor destroyed.
Atoms won’t change their identity (e.g. a
Carbon atom can’t become an Iron atom)
This means that you have to have the
same number of each type of atom on each
side of the chemical equation.
Chemical Equations
Because of the principle of the
conservation of matter,
An equation must be balanced
It must have the same number of
atoms of the same kind on both sides.
Types of Chemical Reactions
*Synthesis – The get together
*Decomposition- The break up
*Single Replacement- The Cheater
*Double Replacement- The Swap
*Combustion - The Lovable
**The Red names are “helpful hints”
Synthesis/Combination
Decomposition
Single Replacement Reactions
Double Replacement Reaction
Double Replacement Reaction
Combustion
How does this analogy break down?
How does this analogy break down?
Let’s look at the
reactions in more
detail
Synthesis reaction (combination)
•
2 or more reactants combine to form a single product
•
can be a combination of metal and a nonmetal forming ionic
compound.
2Mg (s) + O2 (g) —> 2MgO (s)
•
can be a combination of nonmetals, producing a covalent
compound.
N2 (g) + 3H2 (g) —-> 2NH3 (g)
addition of 2 compounds
SO3 (g) + H2O (l) —-> H2SO4 (aq)
Decomposition/Analysis
•
reverse of synthesis reactions
•
decomposition of ionic compounds
2CuCl2 (s) —-> 2Cu(s) + Cl2(g)
•
dissociation of covalent bond into its nonmetallic
element
2H2O(l) —-> 2H2(g) + O2 (g)
Single Replacement/Substitution
A metal replaces a hydrogen.
Mg (s) + HCL (aq) —-> MgCl2 (aq) + H2 (g)
A more active free metal replaces less active one in a
compound.
Mg (s) + CuSO4 (aq) —> MgSO4 (aq) + Cu (s)
Mg (s) + NaCl (aq) —-> NO REACTION
A nonmetal X can also replace another nonmetal in a
compound.
2NaBr (aq) + Cl2 (aq) —-> 2NaCl (aq) + Br2 (g)
NaCl (aq) + Br2 (g) —-> NO EACTION
Activity Series
•
The most active metals are at
the top. These will replace
metals below them.
•
The halogens are also listed in
order of most active at the top
to least active at the bottom.
•
More active elements replace
less active elements in single
replacement reactions
•
Double Replacement/Metathesis
occurs when 2 ionic compounds exchange cations and
anions with each other.
AgNO3 (aq) + NaCl (aq) —> NaNO3 (aq) + Ag Cl (s)