Download Introduction to Chemical Reactions

Introduction to
Chemical Reactions
{
Types of Chemical Reactions
All content by HST Educational Innovations © 2012. All rights reserved. Use of this material is invited with proper attribution to the source.
Chemical Reactions






Matter is combined or broken apart to form a new type of
matter
Bonds are broken, atoms rearranged, and new bonds are
reformed
Chemical reaction is a change in which one or more
substances are converted into new substances
The substances that react are called reactants
The new substances produced are called products
This relationship can be written as:
Produce
Reactants
Products
All content by HST Educational Innovations © 2012. All rights reserved. Use of this material is invited with proper attribution to the source.
Evidence (signs) of a Chemical
Reaction

Release of a gas


Change in temperature



Evidence - solution changes color
Formation of a precipitate


Evidence – Temperature goes up (exothermic)
Evidence – Temperature goes down (endothermic)
Change in color


Evidence - Bubbles
Evidence - forms and settles to the bottom
Energy is released

Evidence - light or sound
All content by HST Educational Innovations © 2012. All rights reserved. Use of this material is invited with proper attribution to the source.
Symbols Used in Chemical
Reactions
Symbol
Meaning of Symbol
(s)
A reactant or product in the solid state; also used to indicate a precipitate
(l)
A reactant or product in the liquid state
(g)
A reactant or product in the gaseous state
(aq)
A reactant or product in an aqueous solution (dissolved in water)
→
Used to indicate the direction of a reaction. Translated as “yields” of “produces”.
All content by HST Educational Innovations © 2012. All rights reserved. Use of this material is invited with proper attribution to the source.
Parts of a Chemical Equation
Reactants
 Yield sign
 Products
 Coefficients
 Subscripts

HgO(s)
Reactants

Hg(l) + O2(g)
Products
“Yields”
Indicates result of reaction
All content by HST Educational Innovations © 2012. All rights reserved. Use of this material is invited with proper attribution to the source.
Types of Chemical Reactions

Synthesis

Decomposition

Single Replacement

Double Replacement

Combustion
All content by HST Educational Innovations © 2012. All rights reserved. Use of this material is invited with proper attribution to the source.
Synthesis Reaction

Generic Form:

Reactants:


A and B are either elements or simple compounds
Products:


A + B → AB
AB is a complex compound formed from A and B
Reaction Mechanism:

The atoms of A and B are bonded together to form a single
new compound
All content by HST Educational Innovations © 2012. All rights reserved. Use of this material is invited with proper attribution to the source.
Examples of Synthesis Reactions
2 Na + Cl2 → 2 NaCl





Sodium atoms and chlorine gas molecules combine to form
a single new product
Sodium chloride is the product of the reaction
2 Mg + O2 → 2 MgO
Magnesium atoms and oxygen gas molecules combine to
form a single new product
Magnesium oxide is the product of the reaction
In a moment, we will also see that this reaction can also be
classified as a combustion reaction
All content by HST Educational Innovations © 2012. All rights reserved. Use of this material is invited with proper attribution to the source.
Decomposition
Reaction

Generic Form:

Reactants:


AB is a complex compound formed from A and B
Products:


AB → A + B
A and B are either elements or simple compounds
Reaction Mechanism:

The compound AB breaks down into its elements or into
simple compounds
All content by HST Educational Innovations © 2012. All rights reserved. Use of this material is invited with proper attribution to the source.
Examples of Decomposition Reactions
2 H2O2 → 2 H2O + O2




Hydrogen peroxide molecules break down to form new
products that are simple molecules
Water and oxygen gas are the products of the reaction
2 KClO3 → 2 KCl + 3 O2
Potassium chlorate molecules break down when heated
to form new products that are simple molecules
Potassium chloride and oxygen gas are the products of
the reaction
All content by HST Educational Innovations © 2012. All rights reserved. Use of this material is invited with proper attribution to the source.
Combustion Reaction

Generic Form:

Reactants:





A + O2 → H2O + CO2
A is a hydrocarbon (a compound of hydrogen and carbon)
O2 is oxygen gas (we will assume more than enough oxygen is
present)
Products:
When combusting a hydrocarbon, the products will always
be water and carbon dioxide
Reaction Mechanism:


The hydrocarbon is oxidized and produces energy
With a hydrocarbon the reaction is generally rapid
All content by HST Educational Innovations © 2012. All rights reserved. Use of this material is invited with proper attribution to the source.
Examples of Combustion
Reactions
C2H4 + 3 O2 → 2 CO2 + 2 H2O

Ethene (also known as acetylene) is a hydrocarbon

When O2 is a reactant, the reaction must be combustion

The products must be water and carbon dioxide
All content by HST Educational Innovations © 2012. All rights reserved. Use of this material is invited with proper attribution to the source.
Single Replacement
Reaction

Generic Form:

Reactants:



A is a metal element
BY is an ionic compound
Products:



A + BY → AY + B
AY is an ionic compound
B is a metal element or a diatomic molecule
Reaction Mechanism:



A and B are elements of the same type
If A is more reactive than B, the reaction occurs with A replacing B
If A is less reactive than B, no reaction can occur
All content by HST Educational Innovations © 2012. All rights reserved. Use of this material is invited with proper attribution to the source.
Examples of Single Replacement
Reactions
2 Al(s) + 3 CuCl2(aq) → 2 AlCl3(aq) + 3 Cu(s)



Aluminum is a metal and copper is the metal in the ionic
compound
Aluminum is more reactive than copper, therefore the
reaction occurs
The aluminum replaces the copper ion in the ionic
compound and the element copper forms as a precipitate
What happens if the reaction is reversed?
Cu(s) + AlCl3(aq) → No reaction occurs

The copper is not more reactive than the aluminum, so no
reaction occurs
All content by HST Educational Innovations © 2012. All rights reserved. Use of this material is invited with proper attribution to the source.
Double Replacement
Reaction

Generic Form:

Reactants:



AX is an ionic compound
BY is an ionic compound
Products:



AX + BY → AY + BX
AY is an ionic compound
BX is a an ionic compound
Reaction Mechanism:



A and B are elements of the same type (both are metals ) as are X and Y
(both are non-metals)
A replaces B and X replaces Y (the ions trade partners)
If an insoluble product (precipitate or insoluble gas) is produced, the reaction
occurs
All content by HST Educational Innovations © 2012. All rights reserved. Use of this material is invited with proper attribution to the source.
Examples of Double Replacement
Reactions
Na2SO4(aq) + Ba(NO3)2(aq) → 2 NaNO3 (aq) + BaSO4(s)



The ions in the two ionic compounds change partners
and form two new ionic compounds
BaSO4 is not soluble in water
BaSO4 is the product of the reaction
What happens if there is no precipitate?
Na2SO4(aq) + KNO3 (aq) → No Reaction


The ions of sodium, potassium, sulfate, and nitrate
cannot produce an insoluble product
Therefore, there is no product of the reaction and that
means there is no reaction between the sodium sulfate
and the potassium nitrate
All content by HST Educational Innovations © 2012. All rights reserved. Use of this material is invited with proper attribution to the source.
Types of Chemical Reactions
Summary
All content by HST Educational Innovations © 2012. All rights reserved. Use of this material is invited with proper attribution to the source.
Key Terms





Combustion Reaction  A + O2 → Oxidized Metal or CO2 + H20
Decomposition Reaction  AB → A+ B
Double replacement Reaction  AX+ BY → AY + BX
Single replacement Reaction  A + BY → AY + B
Synthesis Reaction  A+ B → AB
All content by HST Educational Innovations © 2012. All rights reserved. Use of this material is invited with proper attribution to the source.