Reaction types
Types of reactions
7.2 Types of Reactions
• 7 types of reactions
• Synthesis: is a reaction in which two or more
substances react to form a more complex
single substance
• A+BC
• Ex. 2 Na + Cl2  2 NaCl
• Decomposition Reaction: is a reaction in
which a compound breaks down into two or
more simpler substances
• ABA+B
• Ex. 2 H20  2 H2 + O2
• Compost pile, digesting food, electrolysis
(breaking down H2O with electricity)
• Combustion Reaction: is reaction where a
substance reacts rapidly with oxygen.
• Flammability or explosiveness
• Ex. CH4 + 2 O2  CO2 + 2 H2O
• Ex. Burning any type of fuel
• Usually produces CO2 (greenhouse gas)
• Oxidation Reaction: are reactions where a
substance reacts slowly with the oxygen in air
or water
• Happens with metals
• “rust” or “tarnish”
• Ex. 2 Ca + O2  2 CaO
• Single Replacement Reaction: is a reaction
where one element takes the place of another
element
• A+BC AC+B or D+BC BD +C
• Cu + 2 AgNO3  2 Ag + Cu(NO3)2
• Double Replacement: is a reaction where 2
elements replace each other
• AB+CDAD+CB
•
CaCO3 + 2 HCl  CaCl2 + H2CO3
Discussion Question:
• What two Chemical reactions are “opposites”
of each other and why?
• Synthesis and decomposition; in synthesis
multiple substances combine to form a new
one, while decomposition a single substance
breaks apart into multiple simpler substances
• Exothermic Reactions: are reactions that
release energy into their surroundings
• Give off heat (exergonic)
• Ex. Combustion Reactions
– Ex. Burning fossil fuels
• Endothermic Reaction: is a reaction where
heat energy is absorbed by its surroundings
• Ice absorbs heat to melt
into water
• Gets colder (endergonic)
• Ex. Ice pack and decomposition of mercury
Energy and reaction rates
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Reaction Rates
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Increasing Reaction Rate:
1. Temperature
2. Surface area
3. Stirring
4. Concentration of Reactants
5. Catalyst: is a substance that affects
reaction rate without being used up.
• Activation energy: What it takes to get a
reaction started
• Inhibitor: Something that stops or inhibits a
reaction from proceeding
• Rate of reaction: how fast a reaction proceeds
Discussion Question:
• How are chemical bonds involved in energy
exchanges?
• Breaking bonds requires energy; forming
bonds releases energy.
What affects the rate of a reaction
• Heat
• Size of particle/ surface area
• Catalysts
What is a catalyst?
• A substance that speeds up a reaction
without being changed by the reaction.
• Enzymes are biological or protein
catalysts.
Reaction Energy
All chemical reactions are accompanied by a change
in energy.
Exothermic - reactions that release energy to
their surroundings (usually in the form of heat)
oΔH (enthalpy) is negative – energy leaving system
Endothermic - reactions that need to absorb heat
from their surroundings to proceed.
oΔH (enthalpy) is positive – energy coming into
the system
Reaction Energy
•Spontaneous Reactions - Reactions that proceed immediately when two
substances are mixed together. Not all reactions proceed spontaneously.
•Activation Energy – the amount of energy that is required to start a
chemical reaction.
•Once activation energy is reached the reaction continues until you run
out of material to react.
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