1 mr. shieldsregents chemistry u03 l01 2 energy in the si system the unit of energy is the joule 1...

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Mr. Shields Regents Chemistry U03 L01

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EnergyIn the SI System the unit of ENERGY is the JOULE

1 “small c” calorie = 4.184 Joules

Another unit of energy is the calorie

Note the little c

1 cal = 4.184J

In our food, Calories are designated on the label by a large C and 1 Calorie = 1000 calories

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What do these units mean?

1 Joule = the energy required to lift a golf ball 1 meter

1 calorie = 4.184 Joules1 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

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So… 1 chocolate bar = approx 230 Calories or 230,000 caloriesor enough energy to heat about 507 lbs of water 1 deg. C !!!

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Energy: The Ability to do Work Potential = Energy of position.

Also called STORED ENERGY

Kinetic = Energy of movement Rememeber: Temp = Avg KE

Electromagnetic = Wave energy. Example: Visible light, microwaves, UV

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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

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Potential EnergyPotential 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

g = gravitational acceleration of the earth (9.8 m/sec2) h = Height or distance between two objects

Note: m (kg) x g = Newtons (N)

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Bonding PE Curve

Separated atoms / High PE

o o

o—oStable Bondmin PE

oo nuclei approach each other high PE

Energy stored in chemical bonds

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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

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Kinetic EnergyKinetic 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?

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Kinetic Energy & TempWhy is KE related to Temperature?

The faster molecules move the more ENERGY they have.

When Molecules collide with the thermometer they transferSome of their energy. As KE increases more energy isTransferred.

As ENERGY is transferred the molecules in the liquid insidethe thermometer speed up and expand.

So… Temperature measures of AVG. KE of all molecules

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Changing KE with Temperature

At higher temperatures molecules are moving at higher velocities

273°

373°

473° Faster molecules

At a given temperature not all molecules are moving at the same speed

Slower molecules

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Hertz

Increasing Energy

Decreasing Wavelength

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(The speed of light)

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Conservation of EnergyCan an matter have kinetic and potential energy?

Consider thisphoto…

Can you explain how water flowing in the dam has both Kinetic and Potential Energy?

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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 wasstored when you ascended up the tower turns continuously intoKinetic Energy. This is an example of the LAW OFCONSERVATION OF ENERGY.

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Conservation of EnergyMolecules can also have both Kinetic and Potential 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

Molecules are in constant motion and thus have KE

- Recall temperature is a measure of this energy

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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) energyStored 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 4. Motion2. Sound3. Light

Is the energy now destroyed once the match burns out?

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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