Transcript types of reactions and energy changes

Types of Reactions
7.2
Classifying Reactions
• reactions are often classified by the type of
reactant or the number of reactants and
products.
• some general types of chemical reactions
are:
• synthesis
• decomposition
• single-replacement
• double-replacement
• combustion
synthesis
• a synthesis reaction is a reaction in
which two or more substances react to
form a single substance:
• Na + Cl ---> NaCl
• 2H + O ---> 2H O
2
2
2
decomposition
• decomposition is a reaction in which a
compound breaks down into two or
more simpler substance. The exact
opposite of synthesis.
• 2H O ---> 2H + O
• CaCO ---> CaO + CO
2
2
3
2
2
single replacement
• a single-replacement reaction is a
reaction in which one element takes the
place of another
• 2K + 2H O ---> H + 2KOH
• Cu + 2AgNO ---> Cu(NO )
2
2
3
3 2
+ 2Ag
double replacement
• a double replacement reaction is one in
which two different compounds
exchange positive ions and form two
new compounds:
• CaCO + 2HCL ---> CaCl + H CO
• Pb(NO ) + 2KI ---> PbI + 2KNO
3
3 2
2
2
2
3
combustion
• a combustion reaction is one in which a
substance reacts rapidly with oxygen,
often producing heat and light.
• CH
4
+ 2O2 ---> CO2 + 2H2O
Energy Changes in
Reactions
7.3
chemical bonds and
energy
• chemical energy is the energy stored in
the chemical bonds of a substance.
• chemical reactions involve the breaking
of chemical bonds in the reactants and
the formation of chemical bonds in the
products.
breaking and forming
bonds
• breaking chemical bonds requires
energy.
• forming chemical bonds releases
energy.
exothermic and
endothermic reactions
• during a chemical reaction, energy is
either released or absorbed.
exothermic reactions
• a chemical reaction that releases
energy to its surroundings is called an
exothermic reaction.
• in exothermic reactions, the energy
released as the products form is greater
than the energy required to break the
bonds in the reactants.
Reaction Energy Exothermic
energy released to
the surroundings
ex: freezing
endothermic reactions
• a chemical reaction that absorbs energy
from its surroundings is called an
endothermic reaction.
• in an endothermic reaction, more
energy is required to break the bonds in
the reactants than is released by the
formation of the products.
Reaction Energy Endothermic
energy is
absorbed from
the surroundings.
ex: melting
conservation of energy
• in an exothermic reaction, the chemical
energy of the reactants is converted
into heat plus the chemical energy of
the products.
• in an endothermic reaction, heat plus
the chemical energy of the reactants is
converted into the chemical energy of
the products.