Transcript Energy stored in chemical bonds

Mr. Shields
Regents Chemistry
U03 L01
1
Energy
In the SI System the unit of ENERGY is the JOULE
Another unit of energy is the calorie
Note the little c
1 “small c” calorie = 4.184 Joules
1 cal = 4.184J
In our food, Calories are designated on the label by a large C
and 1 Calorie = 1000 calories
2
What do these units mean?
1
1 Joule = the energy required to lift a golf ball 1 meter
1 calorie = 4.184 Joules
1 calorie (or 4.184 J) can raise the temp of 1g water 1°C
1 Calorie can raise 1Kg (2.54lbs.) of water 1°C
So… 1 chocolate bar = approx 230 Calories or 230,000 calories
or enough energy to heat about 507 lbs of water 1 deg. C !!!
3
Energy: The Ability to do Work

Potential = Energy of position.


Kinetic = Energy of movement


Also called STORED ENERGY
Rememeber: Temp = Avg KE
Electromagnetic = Wave energy.

Example: Visible light, microwaves, UV
4
Temperature vs Heat

Temp is a measure of the average kinetic energy
of the particles of a substance.

Temperature does not measure total energy
 Temperature does not depend on amount of a
substance present; Heat (q) does.

Ex. 70° Swimming Pool vs. 70° Cup of Tea
 Temp is the same but there is more heat
energy (q) in the swimming pool
5
Potential Energy
Potential energy is the energy of position.
It exists whenever two things are separated by some distance
Ex: Man on a cliff, planets and the sun, any assembly of objects
PE = mg x h
Note: m (kg) x g = Newtons (N)
g = gravitational acceleration of the earth (9.8 m/sec2)
h = Height or distance between two objects
6
Bonding PE Curve
Energy stored in chemical bonds
oo
nuclei
approach each other
high PE
Separated atoms /
High PE
o
o
o—o
Stable Bond
min PE
7
Stability and Energy

If PE is high, stability is low.



You standing on the edge of a cliff
Two highly separated atoms
If PE is low, stability is high.


You standing at the bottom of the cliff
Two atoms joined together in a bond
8
Kinetic Energy
Kinetic Energy is the energy of mass in motion.
Everything you see moving has kinetic energy.
- KE increases as mass and speed increase
The equation for KE is…
KE = (1/2) m v2
What kind of curve is this?
9
Kinetic Energy & Temp
Why is KE related to Temperature?
The faster molecules move the more ENERGY they have.
When Molecules collide with the thermometer they transfer
Some of their energy. As KE increases more energy is
Transferred.
As ENERGY is transferred the molecules in the liquid inside
the thermometer speed up and expand.
So… Temperature measures of AVG. KE of all molecules
10
Changing KE with Temperature
At a given temperature not all molecules are moving at the same speed
273°
Slower molecules
373°
473°
Faster molecules
At higher temperatures molecules are moving at higher velocities
11
Decreasing Wavelength
Hertz
Increasing Energy
12
(The speed of light)
13
Conservation of Energy
Can an matter have kinetic and potential energy?
Consider this
photo…
Can you explain how
water flowing in the dam
has both Kinetic and
Potential Energy?
14
The Law of Conservation of
Energy
You sit in a elevator like cart which is
pulled all the way to the top of the tower.
It lurches to a stop ... and then swoosh
you're dropped down. Explain the
change in energy.
As you drop down the track all the Potential Energy that was
stored when you ascended up the tower turns continuously into
Kinetic Energy. This is an example of the LAW OF
CONSERVATION OF ENERGY.
15
Conservation of Energy
Molecules can also have both Kinetic and Potential Energy.
Molecules are in constant motion and thus have KE
- Recall temperature is a measure of this energy
Atoms in molecules vibrate along their chemical bonds
- The chemical bond itself stores PE (like a spring)
- As the atoms vibrate back and forth PE is converted
to KE and vice versa
16
Let’s Apply the law of conservation of energy to a match.
What kind of Energy does the match have?
Initially the match had only potential (chemical) energy
Stored in its bonds. What happens when I strike it?
- When it’s struck the friction creates heat
- The heat provides energy to break bonds
- When we break chemical bonds we create…
1. Heat
2. Sound
3. Light
4. Motion
Is the energy now destroyed once the match burns out?
17
Conservation of Energy
Simply restated
The LAW OF CONSERVATION OF ENERGY SAYS
Energy can neither be created nor destroyed
The energy of the universe is conserved
18