Download Chapter 5 – Chemical Reactions

Chapter 5 – Chemical Reactions
Nuclear change – change in the nucleus of an
atom (This will cause one element to change
into another.)
Examples: nuclear power plants, atomic bombs
or radioactive decay
Physical change – no new chemical produced
Examples: melting or boiling
change of particle size
Chemical Change – when a chemical reaction
produces a new (different) chemical
Examples: Burning paper
Rusting iron
Vinegar and baking soda
How do we know if a chemical
reaction has taken place?
Clues
1.
2.
3.
4.
Color change
Heat given off
Gas produced
Solid formed when two liquids are mixed
(precipitate)
5. A different smell
Chemical Equation
H2 +
O2
Reactants
(what you start with)
H2O
Products
(what you end up with)
A chemical equation tells you what
compounds you start with and what
compounds you end up with.
A balanced chemical equation
also tells you how much of each
material you need.
2H2 +
O2
2H2O
For every one oxygen we need two
hydrogen and we get two water
molecules
An equation is balanced if you have the same
number of each kind of atom on each side.
Na
+
Cl2
NaCl
Not Balanced
Balancing equations
Rule 1 – Balance equations by placing
coefficients in front of the formulas.
Rule 2 – Do not change the subscripts of
the formulas.
2 Na
Balanced
+
Cl2
2 NaCl
Types of Chemical Reactions
Synthesis
A + B
AB
Two substances are combined to form a
third substance.
Na + Cl
NaCl
Decomposition AB
A + B
Breaking apart one substance into two
substances. This is the opposite of a
synthesis reaction
NaCl
Na + Cl
Draw a diagram of each reaction
1.
C + O2
CO2
2.
2 P + 3 Cl2
2 PCl3
3. N2 + 3 H2
4. CH4 + 2 O2
2 NH3
CO2 + 2 H2O
Types of Chemical Reactions
Single Replacement A + BC
AC + B
One element replaces another in a compound.
A more reactive element will always replace
a less reactive element.
F + NaI
NaF + I
+-
+-
Double Replacement AB + CD
AD + CB
Elements exchange partners to form different
compounds.
+-
+
-
HCl + NaOH
+ -
+
-
HOH + NaCl
Factors affecting the rate of
reactions
Particle size – the smaller the particles the
faster the reaction (example – dust explosion)
Higher temperature – the higher the
temperature the faster the reaction
Increase concentration of solution (a more
concentrated acid will react faster than a dilute
acid)
Add a catalyst – a catalyst is a chemical that
speeds up a reaction but does not get used up
by the reaction
Predicting Chemical Reactions
If two elements are being combined the
reaction will be synthesis.
Two metals will not combine chemically
Noble gases will not combine
Write the symbol for the more positive
element first and then use the criss-cross
method to determine the formula.
Predicting Decomposition
Reactions
If there is just one compound, the only
thing it can do is decompose (break down)
This often requires energy
If a product is a diatomic molecule you
must place a 2 after the element symbol.
(The diatomic molecules are marked on
your chart.)
Predicting Single Replacement
Reactions
If there is an element and a compound, the
reaction will be a single replacement.
A more reactive metal will replace a less
reactive metal or hydrogen.
The more reactive metals are located near
Cs and Fr on the chart.
A more reactive non-metal will replace a less
reactive non-metal.
The more reactive non-metals are near F on
the chart.
Predicting a Double Replacement
Reaction
If there are two compounds containing
positive and negative groups, the reaction
will be a double replacement.
A double replacement reaction will take
place if there is a very stable compound
such as HOH produced.