Unit 07 Notes
(Ch.8 in textbook)
Chemical Reactions
Additional vocabulary:

Acid-Base Reactions - Also called a neutralization reaction; occurs
when an acid reacts with a base. They are considered one type of
double-replacement reaction. Products will be a salt and H2O.

Precipitation Reactions – Occurs when two soluble ionic compounds
react to form an insoluble product, the precipitate. Precipitates form
when the electrostatic force of attraction between the ions is greater
than the tendency of the ions to stay in solution. They are common in
both nature and industrial processes. A type of double-replacement
reaction.

Phlogiston - A hypothetical substance formerly thought to be a
volatile constituent of all combustible substances, released as flame in
combustion.
Father of Mother of Modern Chemistry
Both lived during 18 th century


Antoine Lavoisier – father of modern chemistry

Lots of research on combustion

Disproved the theory of phlogiston
Marie-Ann Lavoisier – mother of modern chemistry

Lab assistant to her husband

Collaborator with her husband

A substance that undergoes a reaction is called a
__________.

Reactants are written on the left of the arrow

These will be the things you start with

When reactants undergo a chemical change, each

new substance formed is called a ___________.

Products are written on the right of the arrow

These are the things that you produce
Chemical Equations
chemical equations—use chemical formulas
and an arrow to separate reactants from
products
Fe + O2
→
Fe2O3
skeleton equation—shows just the formulas;
does not show the relative amounts of
reactants and products used in the reaction
States of Matter and Symbols

Use symbol to show the state of matter

(s) __________

(l) __________

(g) __________

(aq) __________ (substance dissolved in water)
Fe (s) + O2 (g) →Fe2O3 (s)
Use of catalysts

many times, a catalyst is employed in a reaction

catalyst—speeds up the rate of reaction but is not
used up in the reaction
(is written above the arrow in equation)
MnO2
2H2O2(aq)

2H2O(l) + O2(g)
Diatomic molecules

Seven elements normally exist as diatomic molecules—
these will always be written as X2 when writing equations

H2

O2

N2

F2

Cl2

Br2

I2

In order to write equations you MUST remember your diatomic
elements…

In a chemical equation the Law of
conservation of matter MUST be observed!

This means the # of atoms of reactants =
the # of atoms of products

What you start with has to equal what you
end with
Balancing Chemical Equations

unbalanced equation—an equation that does
not indicate the quantity of the reactants
needed to make the products

balanced equation—gives the correct quantity
of each reactant and product—each side of the
equation has the same number of atoms of
each element

coefficient—numbers placed in front of the
symbols
Steps for Balancing Chemical Equations
1.
Write the symbols for the reaction
2.
Count the number of atoms of each element of the
reactants.
3.
Count the number of atoms of each element of the
products.
4.
Add / Change the coefficient to make the numbers of
each element equal.
5.
YOU CAN NEVER CHANGE A SUBSCRIPT !
6.
Write the coefficients in the lowest possible ratio.
7.
Check your work.
Types of Reactions

There are 5 major classifications of reactions:

Synthesis (or Combination)
A + B  AB

Decomposition
AB  A + B

Combustion
A + O2(g)  AO2

Single Replacement
A + BC  AC + B

Double Replacement
AB + CD  AD + CB
Flash cards:
Using the piece of paper given to you, write the name of each
reaction type in a separate box. On the back side of the paper,
write the sample equation on the corresponding area for each
reaction type. As you have time, cut out the cards for studying.
Examples of Synthesis Reactions

Metal + Nonmetal
2Na+ Cl2  2 NaCl

Two nonmetals
S + O2 SO2

Nonmetal oxide + water  acid
SO2 + H2O H2SO3

Metal oxide + water  base
CaO + H2O Ca(OH)2
 Example of Decomposition Reactions
CaCO3 CaO + CO2
 Examples of Combustion Reactions
2Mg + O2  2 MgO
C3H8 + 5O2  3CO2 + 4H2O
Single Replacement Reactions

Also called Single Displacement Rxn.
Example:
Cu + 2AgNO3  2 Ag + Cu(NO3)2
Metals
Whether or not one metal will replace another can be determined by
consulting the Activity Series of Metals. A reactive metal will replace any
metal BELOW it in the activity series.

In order for the reaction to occur, the lone element must be
above the element in the compound

Otherwise…NO REACTION
Will the following reactions occur? If so, complete and balance the
reaction.
Ag + Cu(NO3)2 
Mg + AlCl3 
Nonmetals

A nonmetal can also displace another nonmetal from a compound. This
replacement is usually limited to the halogens (group 7A) and the
reactivity decreases as you go down the periodic table.
Will the following reactions occur? If so, complete and balance
the reaction.
Br2 + MgCl2 
F2 +
MgCl2 
Double Replacement Reactions

Also called Double Displacement Reaction

Anions of two different compounds switch places, forming two new
compounds.

Generally occur between two ionic compounds in aqueous solution
and usually form a

precipitate,

gas, or

molecular compound
Example: Na2CO3 + 2AgNO3  2NaNO3 + Ag2CO3