Mr Shields Regents Chemistry U 03 L 01

Mr. Shields Regents Chemistry U 03 L 01 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. 184 J 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 1 g water 1°C 1 Calorie can raise 1 Kg (2. 54 lbs. ) 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 n Potential = Energy of position. n n Kinetic = Energy of movement n n Also called STORED ENERGY Rememeber: Temp = Avg KE Electromagnetic = Wave energy. n Example: Visible light, microwaves, UV 4

Temperature vs Heat n Temp is a measure of the average kinetic energy of the particles of a substance. n Temperature does not measure total energy n Temperature does not depend on amount of a substance present; Heat (q) does. n Ex. 70° Swimming Pool vs. 70° Cup of Tea n 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/sec 2) 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 n If PE is high, stability is low. n n n You standing on the edge of a cliff Two highly separated atoms If PE is low, stability is high. n n You standing at the bottom of the cliff Two atoms joined together in a bond 8

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 v 2 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 thermometer they transfer Some of their energy. As KE increases more energy is Transferred. As ENERGY is transferred the molecules in the liquid inside 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