Transcript Lesson 11 Matter, Energy, and Changes

Lesson 11 Matter,
Energy, and Changes
1. Forms of Energy
a.
b.
c.
Energy is the ability to do work.
There are two general types of energy.
Kinetic energy is the energy of motion:
i.Kinetic energy is energy that moving
objects possess by virtue of their motion.
ii. The amount of energy in an object,
depends on the mass and the velocity of the
object, according to the following formula:
KE = ½(mass)*(velocity)2
iii. KE is measured in units of kg*m2/s2
iv. This formula is used extensively in
physics
b.
Potential Energy is stored energy.
i. Potential Energy is energy that an object
possesses because of its position – it is
also known as stored energy.
ii. This energy corresponds to the amount of
energy required to keep the object in that
position.
iii. Objects in an elevated position possess
potential energy – the higher the object the
more potential energy is possesses.
iv. Position does not only include height:
1. A spring in a watch can possess
potential energy, because of the fact
that is is coiled into a specific
“position”.
2. Chemicals can possess potential
energy because of the position of
the elements which make them up
and the ways in which they are
bonded.
3. Example: ATP
c.
Changes in Energy
i. Energy can change from one type to
another - such as kinetic to potential.
ii. Example: Swinging Person
at the top of each trip forward or
back, the person momentarily is at
rest and possesses potential
energy
iii. Endothermic: changes which
absorb heat when they occur –
melting, boiling, and cooking are
examples
iv. Exothermic: reactions which give
off heat when they occur –
condensation, freezing, and a
chemical heat pack are
examples.
v. Keep in mind that the change we are looking at is
the internal change in energy.
1. For some of these, it is easy to predict- for
example a fire is exothermic because you can
feel the heat coming out of the reaction.
2. For others, it is more difficult. Consider
the following:
a. chemical ice pack: gets cold
because it absorbs the heat from
around it – therefore it is endothermic.
b. cooking a chicken – the food gets
warm inside and the heat going in
causes chemical reactions – therefore
it is endothermic.
c. Water freezing – the water gets
cooler, giving off heat energy to the air
around it- therefore it is exothermic.
II. Relating Mass and Energy:
a.
Mass is a form of energy
i. Einstein discovered the relationship between
mass and energy:
1. Formula: E = mc²
2. Explanation: E = energy
m = mass
c = speed of light
3. In other words, a very large amount of
energy is contained in a very small
amount of matter
b. Energy cannot be created or destroyed
i. Energy can be transformed from one kind to
another.
ii. Energy can be transferred between objects.
iii. Law of Conservation of Energy: energy
can neither be created or destroyed; it can only
change form.
iv. The total amount of energy in the universe
remains constant.
v. The total amount of energy in a closed system
also remains constant.
vi. Law of Conservation of Mass: mass
cannot be gained or lost in a normal chemical
reaction.
vii. Our are of study will be normal chemical
reactions, so this law is VERY IMPORTANT!
Demonstration of the Law of
Conservation of Mass
III. Matter Changes
a.
Physical Changes do not affect chemical
compostion
i. Physical changes are changes that only affect
physical properties.
ii. Chemical properties are unaffected.
iii. Some examples of physical changes:
1. Breaking something into smaller
pieces.
2. Mixing things together that do not
react. (such as sand and iron filings)
3. State Changes
b. Chemical changes alter chemical
composition
i. Chemical change: a change where one
or more new substances are produced.
ii. The total number of atoms does not
change.
iii. Signs of a chemical reaction: (although
not proof)
1. Bubbles
2. Formation of a precipitate
3. Heat
4. Light
5. Color change
ii. All chemical changes involve some
transfer of energy.
iii. Examples of chemical changes:
1. Burning
2. Digestion
3. Acid/Base reactions
4. Building of glucose molecules by
photosynthesis
DEMONSTRATIONS
Endothermic, Exothermic, Physical,
and Chemical Reactions
Demonstrations:



Acid and Metal
Ammonium Nitrate
and water
Salt water separation
Common Pitfalls
Students often confuse chemical and
physical changes, because they
think that they are mutually
exclusive, ie. Not able to be present
at the same time. Often times, a
chemical change, such as burning, is
accompanied by physical changes,
such as color change. Keep this in
mind as you think about what
happens during these two types of
changes!
Questions:
1. Compare and contrast the two different
types of energy.
2. What is the equation, and the meaning of
the variables in it, that relates matter to
energy?
3. Define the law of conservation of mass,
and the law of conservation of energy.
4. Draw a diagram relating the three
common states of matter, and the names
for the changes among them.
5. List the five signs that indicate a
chemical reaction may have taken place.
6. Indicate which type of change each of the
following indicates, both physical/chemical
and endothermic/exothermic.
Item
Cooking a chicken
A campfire
Breaking a ruler
Boiling water
Using a chemical ice pack
Painting a house
Dew condensing on grass
Firecracker exploding
Photosynthesis
Physical/Chemical
or both
Endorthermic
or Exothermic
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