Chemical
Reactions
Interest Grabber
Section 2-4
Matter and Energy
Have you ever sat around a campfire or watched flames flicker in a
fireplace? Roasted marshmallows?
The burning of wood is a chemical reaction—a process that changes
one set of chemicals into another set of chemicals.
A chemical reaction always involves changes in chemical bonds that
join atoms in compounds. The elements or compounds that enter
into a chemical reaction are called reactants. The elements or
compounds produced by a chemical reaction are called products.
As wood burns, molecules of cellulose are broken down and
combine with oxygen to form carbon dioxide and water vapor, and
energy is released.
I. Chemical Reactions
A. process that changes or transforms one set of chemicals
into another
B. always changes the chemical bonds that join atoms in
compounds
C. during chemical transformations mass and energy are
conserved
1. also true for chemical reactions
D. some reactions occur slowly
1. example
a. combining iron and oxygen to
form iron oxide (rust)
b. silver tarnishing
E. some reactions occur quickly
1. example
a. a match burning
b. a cake rising (from baking soda or
baking powder)
A chain rusting is a ______.
1. Chemical change only
2. Physical change only
3. Both a chemical &
physical change
4. Neither a chemical or
physical change
A roasted a marshmallow is a ____.
1. Chemical change only
2. Physical change only
3. Both physical &
chemical changes
4. Neither a physical nor
chemical change
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F. reactants
1. the elements or compounds that enter into a
chemical reaction
G. products
1. the elements or compounds that are
produced by the chemical reaction
What are the reactants when wood
burns?
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2.
3.
4.
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Cellulose & O2
CO2 & H2O
Cellulose & H2O
Cellulose & CO2
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What are the products when
wood burns?
1.
2.
3.
4.
Cellulose & CO2
Water & CO2
Cellulose & O2
CO2 & O2 & H2O
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H. living organism body chemical reaction
1. involves carbon dioxide
a. cells actively produce CO2 which
travels through your body til you
exhale it, however it is not very
soluble in water
b. when CO2 enters bloodstream reacts
to water and produces carbon
acid
c. once it enters your lungs, it reacts
again and turns into CO2 gas for
you to exhale
II. Energy in reaction
A. every time a bond is broken, energy is released
B. since chemical reactions involve breaking & forming
bonds, they involve changes in energy
C. energy changes
1. energy can be released or absorbed
2. can occur spontaneously
3. if energy is absorbed a chemical reaction
will not occur w/o a source of energy
a. Example 1
1 – hydrogen gas burning (reacting) w/ oxygen to get water
vapor
2 – energy is release in form of heat
(if gas explodes – will also produce sound & light)
b. example 2
1 – reverse reaction
2 – changing water to hydrogen & oxygen gas
3 – a great absorption of energy occurs/needed
i - need an electrical current to separate the
hydrogen and oxygen gas atoms
What type of energy is given off
when wood burns?
1.
2.
3.
4.
5.
Light
Heat
Sound
All of these
None of these
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Do all organisms need chemical
reactions?
1. Yes
2. No
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4. Organisms need reactions that require energy to stay
alive
a. organisms must have a source of energy though
1 – plants get the energy by trapping &
storing sunlight
2 - animals get the energy from eating other
plants/animals
b. energy is released to grow, metabolize, break
down & digest food
D. activation energy
1. not all chemical reactions that require energy
happen spontaneously
a. if so flames or explosions could occur
2. activation energy
a. the energy needed to get a reaction
started
b. a factor in whether the reaction is
released or absorbed
Wood doesn’t burn all by itself. What must you
do to start a fire? What does this mean in terms
of energy?
To start a fire, you must light it with a match
and kindling. You are giving the wood some
energy in the form of heat.
Once the fire gets started, it keeps burning. Why
don’t you need to keep restarting the fire?
Once the fire gets going, it gives off enough
heat to start more of the wood burning.
Energy Absorbing Reaction
Energy Releasing Reaction
products
Activation energy
Activation energy
reactants
reactants
products
www.phschool.com
Web code: cbp-1024
III. Enzymes
A. some reactions are too slow or have activation
energies that are too high to be practical
for tissue
1. need catalysts to make process
possible
a. substance that speeds up the
rate of a chemical reaction
2. works by lowering the reaction’s
activation energy
B. Enzymes
1. proteins that act as biological catalysts
2. enzymes speed up chemical reactions that take place in cells
3. each enzymes handles only one specific reaction type
C. lowering the activation energy has an effect on how quickly the
reaction takes
D. example 1
1. CO2 + H2O = H2CO3
a. if left alone this would produce too much carbon
dioxide than can handle at once
b. your body produces an enzyme called carbonic
anhydrase to help speed up the reaction
by 10 million
IV. Enzyme Action
A. how does it work
1. reactants must collide w/ enough energy to
existing break bonds & create new one
B. enzyme-substrate complex
1. enzymes provide a place where reactants can
be brought to react together
a. site given reduces the amount of
energy needed
C. Substrate
1. reactants of enzyme-catalyzed reactions
D. example
1. enzyme – hexokinase
a. substrates are glucose & ATP
b. during reaction a phosphate is transferred from
ATP molecule to the glucose molecule
c. the substrates then bind on the enzyme at an
active site
1 – the shapes are complementary so they
fit like a lock & key
2 – the enzyme & substrate the bind by
intermolecular forces & form an
enzyme-substrate complex
d. this complex stays bounded until the reaction is
done then the 2 are released so the
process can happen again
*** see video
E. regulation of enzyme activity
1. variables, like in experiments, can affect a chemical reaction
a. temperature, pH levels …
2. enzymes work best at certain pH values
3. temperature – best at 37 degrees C – normal body temperature
a. when ill enzymes not properly functioning
4. cells regulate the activities of enzymes in many ways
a. proteins in cells turn on/off the enzymes at
critical stages in the cell’s life
1 – help regulate chemical pathways
2 – make materials cells need
3- release energy
4 – transfer info
What is the relationship between enzyme
concentration & reaction rate
1. The reaction rate decreases
w/ increasing enzyme
concentration.
2. The reaction rate increases
w/ decreasing enzyme
concentration.
3. Reaction rate increases with
increasing enzyme
concentration.
4. The variables are not directly
rated.
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An enzyme speeds up a reaction by
1. lowering the
activation energy.
2. raising the
activation energy.
3. releasing energy.
4. absorbing energy.
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In a chemical reaction, a reactant bind to an enzyme at
a region known as the
1.
2.
3.
4.
5.
catalyst.
product.
substrate.
active site.
reactive site.
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