Transcript Types of Chemical Reactions

Types of Chemical Reactions
There are five main types of chemical
reactions that we will be covering in this
chapter:
– Combination reactions
– Decomposition reactions
– Single-Replacement reactions
– Double-Replacement reactions
– Combustion reactions
Combination Reactions
In a combination reaction, two or more
substances combine to form a single
substance.
General Equation:
R + S  RS
Example:
Mg(s) + O2 (g)  MgO(s)
Decomposition Reactions
In a decomposition reaction a single
compound is broken down into two or
more products.
General Equation:
RS  R + S
Example:
HgO(s)  Hg(l) + O2
Single-Replacement Reactions
In a single-replacement reaction, one
element replaces a second element in a
compound.
General Equation:
T + RS  TS + R
Example:
K(s) + H2O(l)  KOH(aq) + H2 (g)
Double-Replacement Reactions
Double-replacement reactions involve an
exchange of positive ions (or cations)
between two reacting compounds. These
reactions generally produce a precipitate,
a gaseous product, or water.
General Equation:
R+S- + T+U-  T+S- + R+UExample:
K2CO3 (aq) + BaCl2 (aq)  BaCO3 (s) + KCl(aq)
Combustion Reactions
In a combustion reaction an element or a
compound (often a hydrocarbon) reacts
with oxygen, often producing energy as
heat and light. The products of these
types of reactions are carbon dioxide and
water.
Example: The combustion of methane
gas in air
__CH4 (g) + __O2 (g)  __CO2 (g) + __H2O(g)
Combustion Reactions
The reaction between some elements and
oxygen is also an example of a combustion
reaction. For example:
__Mg(s) + __O2 (g)  __MgO(s)
Here Mg acts as the fuel for the reaction and
when reacted with O2 (g) will for an oxide – in this
case magnesium oxide (MgO(s)). What other
type of chemical reaction does this look like?
Combination Reactions
Complete and balance the following
combination reactions:
Be + O2 
H 2 + O 2  H 2O
Decomposition Reactions
Complete and balance the following
decomposition reactions:
HI 
Mg(ClO3)2  MgCl2 +
Single-Replacement Reactions and
Activity Series
For example:
Mg(s) + Zn(NO3)2 (aq) 
Mg(s) + AgNO3 (aq) 
Mg(s) + LiNO3 (aq) 
Single-Replacement Reactions
Complete the equations for the following single
replacement reactions that take place in aqueous
solution. Balance each equation. If a reaction does
not occur (use activity series) write “no reaction.”
Fe(s) + Pb(NO3)2 (aq) 
Cl2 (g) + NaI(aq) 
Ca(s) + H2O(l) 
Double-Replacement Reactions
and the Solubility Rules
Mixing the solutions of two ionic compounds can
sometimes result in the formation of an insoluble
salt called a precipitate.
In order for a double-replacement reaction to
occur there must be fewer ions in solution when
the two compounds are mixed. Otherwise all we
have is a mixture.
Recall our conductivity demo – when ionic
compounds dissociate they can conduct
electricity.
Double-Replacement Reactions
We also have fewer ions in solution if we
produce a gas or water.
Double-Replacement Reactions
Write the products for the following
reactions. Then balance each equation.
NaOH(aq) + Fe(NO3)3 (aq)
Ba(NO3)2 (aq) + H3PO4 (aq)
Double-Replacement Reactions
and the Solubility Rules
Should a precipitate form when aqueous
solutions of Na2SO4 (aq) and Ba(NO3)2 (aq)
are mixed?
Double-Replacement Reactions
and the Solubility Rules
Should a precipitate form when aqueous
solutions of NaCl(aq) and Zn(NO3)2 (aq) are
mixed?
Combustion Reactions
Predict the product of the following
combustion reaction:
S(s) + O2 (g) 
Combustion Reactions
Write a balanced equation for the
complete combustion of each compound.
– Heptane (C7H16)
– Glucose (C6H12O6)
Rates of Reaction
There are three main factors that effect the
rates of chemical reactions:
– The presence of a catalyst
– Temperature
– Concentration
Catalysts
The presence of a catalyst in a chemical
reaction will speed up the reaction while
not being used up in the reaction itself.
Because a catalyst is neither a reactant
nor a product, its formula is written above
the yields sign () in a chemical equation.
Catalysts
For a reaction to occur between two
substances (or reactants) particles of
those substances must collide. Not only
that, they must hit each other with enough
force to cause a change to take place.
The amount of energy the particles must
have when they collide is called the
Activation Energy.
Catalysts are used to lower activation
energy.
Temperature
Most reactions go faster at high
temperatures.
– Ex: Baking a cake speeds up the reactions
that change the liquid batter into a spongy
product.
Lowering the temperature slows down
most reactions.
– Batteries tend to last longer if they are kept
cool, slowing down the reaction that takes
place within them.
Concentration
Concentration – The amount of substance
present in a certain volume.
Raising the concentration of a reactant will
speed up a reaction because there are
more particles per volume.
More particles = more collisions = increase
in reaction rate.