Chemical Reactions
By Zanman
Chemical Reaction Basics



The substances initially
involved in the chemical
reactions are called the
reactants.
Unlike a reactant, though, a
catalyst increases the rate
of a chemical reaction but is
not consumed.
A chemical reaction
produces one or more
products, which most of the
time have different
properties than the
reactants.
 Only the electrons are
affected in a chemical
reaction.
 During a chemical
reaction, chemical
bonds are either made
or broken.
http://en.wikipedia.org/wiki/Image:Hydrochloric_acid_ammonia.jpg
Signs of a Chemical Reaction
There are several
signs to tell that a
chemical reaction
has taken place.
3. A gas is produced
1. A change in temperature
http://amazingrust.com/Experiments/how_to/Images/Chlorine_gas.jpg
4. Precipitate forms
http://www.carnicom.com/sheil/beaker2.jpg
http://www.dkimages.com/discover/previews/857/35080206.jpg
2. A change in color
5. Energy is produced
http://z.about.com/d/chemistry/1/G/5/a/demonstration.jpg
http://www.scienceproject.com/projects/intro/intermediate/images/IC003.jpg
The Law of Conservation of Mass
The Law of Conservation of Mass says that the of mass
a closed system will remain constant, regardless of the
processes acting inside the system.
Basically, it says that matter cannot be destroyed or
created.
This relates to chemical reactions because it means that
even though a chemical bond is forming or breaking, the
matter in the reaction is staying the same.
Energy & Chemical Reactions
A chemical reaction can absorb energy and cool down. An
endothermic reaction is a chemical reaction that does this.
•Photosynthesis is an example of an endothermic reaction
•dissolving ammonium chloride in water
•reaction of barium hydroxide octahydrate crystals with dry
ammonium chloride
http://chemistry.about.com/cs/generalchemistry/a/aa051903a.htm
Or it can release energy and heat up. An
exothermic reaction is a chemical reaction that
releases heat.
reactants → products + energy
Example:
•Na(s) + 0.5Cl2(s) = NaCl(s)
• Sodium and chlorine to make table salt,
which produces 411 Kj of energy for every
mole of salt produced.
•C3H8 + 5O2 ---> 4H2O + 3CO2 + energy
• propane + oxygen yields water + carbon
http://www.popsci.com/files/imagecache/photogallery_image/files/articles/salt_ss_fire2.jpg
dioxide + energy
Energy
http://www.cobb.k12.ga.us/~simpson/Teacher%20Sites/Teacher%20Sites/Electricity.jpg
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Activation energy is the minimum amount of energy needed to
get molecules and/or atoms to start a reaction.
Energy is always released or absorbed in a chemical reaction,
but never destroyed or created.
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
This is called the Law of Conservation of Energy
Also called midnight energy.
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Examples:


When bonding chlorine and sodium, you need to add water first.
This amount of energy is the activation energy.
Boiling water needs to reach a temperature of 212oF in order to boil,
so the amount of energy it takes to get the water to 212oF would be
the activation energy.
 http://wiki.answers.com/Q/How_is_energy_involved_in_chemical_and_physical_changes
 http://en.wikipedia.org/wiki/Activation_energy
 http://discover.edventures.com/functions/termlib.php?action=&termid=173&alpha=a&searchString=
Chemical Potential Energy


Chemical potential energy is a form of potential energy related to the
arrangement of atoms and molecules, which could be the result of chemical
bonds within the molecule.
Chemical potential energy can be transformed into other forms of energy by a
chemical reaction.
Examples:
When a fuel goes through
combustion, the chemical energy is
transformed into heat.
Photosynthesis turns solar energy to
chemical energy.
When methane molecules hits
oxygen atoms at high speeds
(caused by a flame, etc.), there is a
rearrangement of the atoms. Two of
the oxygen atoms will combine with http://www.chemistryland.com/CHM107/Energy/M
the four hydrogen (H) atoms to form ethaneCombustWhiteSimple.jpg
two water molecules (H2O). The
other two oxygen atoms will
combine with methane's carbon
atom to form carbon dioxide.
Types of Reactions:
There are several different types of
reactions. They are:
 Synthesis
 Decomposition
 Combustion
 Single Replacement
 Double Replacement
All of the slides mentioned here use info from:
http://www.usoe.k12.ut.us/curr/science/sciber00/8th/matter/sciber/chemtype.htm
http://www.oralchelation.com/technical/images/atom2.jpg
Synthesis
Synthesis is a type of reaction that combines two chemicals
together in a chemical reactor to get one or more products.
 By looking at the formula, you will see that the two elements
that were before alone are now bonded together into a
compound.
Examples:
 2Na + Cl2 → 2 NaCl (formation of table salt)
 S + O2 → SO2 (formation of sulfur dioxide)
 4 Fe + 3 O2 → 2 Fe203 (iron rusting)
 CO2 + H2O → H2CO3 (carbon dioxide dissolving and

reacting with water to form carbonic acid)
http://www.dtsc.ca.gov/PollutionPrevention/images/chemicals.JPG
Decomposition
 Decomposition is when a more complex
substance breaks down into its simpler parts.
 It is basically the opposite of synthesis.
 By looking at the equation, you will see that
the elements in the compound are now
uncombined and are alone.
Example:
2H2O  2H2 + 02
http://www.zamondo.com/images/lrg_Decomposition.jpg
Combustion
 Combustion is when a fuel and an oxidant react
exothermically with the productions of heat and light
(Flames, or a glow).
 Basically, combustion is when something burns.
http://www.freefoto.com/images/33/15/33_15_10---Fire-Flame-Texture_web.jpg
http://www.boygeniusreport.com/wp-content/uploads/image/explosion.jpg
Single Replacement
 In a single replacement reaction, one uncombined
element replaces a single element in a compound
 It yields two products
 If you look at the equation, then you will see that
one of the elements from the compound is alone
and the element that was alone before is now in
the compound.
Example:
Zn + 2HCl  ZnCl2 + H2
Double Replacement
In a double replacement, two compounds switch their elements to form two
new compounds
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It creates two new products
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If you look at the reaction, then you will see that the elements of the first
compound and the second compound are with different elements than before.
Example:

AB + CD  AC + BD
Combining lead (II) nitrate and potassium iodide
1. Add the potassium iodide to the
beaker.
2. Pour the lead (II) nitrate into the
beaker.
3. Without splashing, stir the contents of
the beaker with the stirring rod for
three minutes.
Pb(NO3)2 (aq) + 2KI (aq) --> 2KNO3 (aq) + PbI2 (s)
http://www.nitrogenorder.org/experiment/dblreplace.shtml
Opening Page Image Credits
Opening Page Image Credits:
• http://chemcarling.googlepages.com/figure-01-39.jpg/figure-01-39-full.jpg
•
http://www.7art-screensavers.com/screens/3d-chemical-elements/borum-atom-quarks.jpg
•
http://grandinetti.org/Teaching/Chem121/assets/caffeine.gif
•
http://facstaff.gpc.edu/~pgore/PhysicalScience/atom-with-electrons.gif
•
http://sub.allaboutcircuits.com/images/00257.png
•
http://www.corrosionsource.com/handbook/periodic/periodic_table.gif
•
http://www.personal.psu.edu/staff/m/b/mbt102/bisci4online/chemistry/structureatoms.jpg
•
http://focus.aps.org/files/focus/v19/st19/water.jpg
Other:
• http://en.wikipedia.org/wiki/
•
http://www.usoe.k12.ut.us/curr/science/sciber00/8th/matter/sciber/chemtype.htm
•
http://answers.yahoo.com/question/index?qid=20081109193239AAsxvbW