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Chemical reaction
Precipitate
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Product
Synthesis
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Single displacement
Double displacement
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Reactant
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Decomposition
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Combustion
Combinations of Matter
(ps lab 065)
When a chemical reaction occurs, there is always a change in the properties and energy content of the
substances involved. There is a change in both the physical and chemical properties as substances are changed
into new substances.
At least one of these should be obvious when a chemical reaction
takes place:
Color change - new substances might reflect different colors of light.
Heat change - the container may get hotter or colder.
Gas produced - bubbles or smoke may be observed.
Precipitate formed - an insoluble solid might form in a liquid.
In order for a chemical reaction to take place, the reactants must have the ability to form chemical bonds.
These bonds are formed by the valence electrons of the reactant atoms. If substances are brought together whose
valence electrons do not match together to complete the Octet Rule, there will be no chemical reaction.
Parts of a chemical reaction:
Reactants •
•
Substances that interact with each
other.
On the left side of the arrow in a
chemical equation.
Products •
New substances formed during a
reaction.
•
On the right side of the arrow in at a
chemical equation.
Reactants
Products
Law of conservation of mass:
During a chemical reaction, atoms are neither created nor destroyed. This means that the number of atoms
remains constant throughout the reaction. Since the number of atoms doesn't change, the mass must remain
constant as well.
There are times when mass might appear to change during a chemical reaction. If you experience this
during an experiment, be sure to remember the law of conservation of mass.
The change in mass must be accounted for in a way other than destroying or creating atoms.
Chemical reaction types:
Chemical
Engineer
We will study these five general types of reactions: synthesis, decomposition, single
displacement, double displacement, and combustion. Once you know these reaction
types, you will be able to look at the reactants of a reaction and predict what products will
be formed.
Two examples are given for each of the reaction types below. You might notice that the same number of atoms
of each element are found on both sides of the reaction arrow. This is accomplished by the added numbers in
front of some of the chemical formulas known as coefficients. They are added to "balance" the equation. You
will learn how to balance equations next week.
Synthesis: two simple substances combine to form a more complex one.
Examples of synthesis reactions:
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The general form is: element + element
2Na + Cl2 2NaCl
4Fe + 3O2 2Fe2O3
compound
Decomposition: a complex substance breaks down into two simple substances.
Examples of decomposition reactions:
•
•
•
The general form is: compound
2H2O 2H2 + O2
H2CO3 H2O + CO2
element + element
Single displacement: a single element replaces an element in a compound.
Examples of single displacement reactions:
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•
•
The general form is: element + compound
Zn + 2HCl ZnCl2 + H2
2Na + 2H2O 2NaOH + H2
compound + element
Double displacement: two different atoms in two different compounds exchange places.
Examples of double displacement reactions:
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•
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The general form is: compound + compound
MgCO3 + 2HCl MgCl2 + H2CO3
2KCl + Pb(NO3)2 2KNO3 + PbCl2
compound + compound
Combustion: a hydrocarbon (molecule containing only carbon and hydrogen atoms) reacts with
oxygen. The products of combustion are always carbon dioxide and water.
Examples of combustion reactions:
•
•
•
The general form is: hydrocarbon + oxygen
CH4 + 2O2 CO2 + 2H2O
C7H16 + 11O2 7CO2 + 8H2O
carbon dioxide + water
Go to chemistry class for more about chemical reactions.
Test Your Concept Understanding:
Identify the "type" for each reaction below:
1. Ca + O CaO
2. Br + LiI LiBr + I
3. Al + Fe(NO3)2 Al(NO3)3 + Fe
4. MgO + HCl MgCl2 + H2O
5. C4H10 + O2 CO2 + H2O
6. NH4NO2 NH3 + H2O
7. (NH4)3PO4 + Sr(OH)2 Sr3(PO4)2 + NH4OH
8. H2SO4 + NaOH Na2SO4 + H2O
9. Zn + AgNO3 Zn(NO3)2 + Ag
10. CuNO3 + KCl KNO3 + CuCl
type of reactions:
1. synthesis
2. single displacement
3. single displacement
4. double displacement
5. combustion
6. decomposition
7. double displacement
8. double displacement
9. single displacement
10. double displacement