TOPIC: ENERGY

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TOPIC ENERGY
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All physical chemical changes are accompanied
by change in energy

• The chemistry of energy changes is known as
  Thermochemistry!

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Stability and Energy

• If energy is high, stability is low
• If energy is low, stability is high

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Energy Ability to do WorkThe SI unit for an
energy measurement is called the Joule
(J)EXAMPLE 1 Joule amount of energy required
to lift a golf ball 1 meter
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Law of Conservation of Energy

• Energy is neither created nor destroyed in
  ordinary chemical or physical change, rather it
  can be converted from one form to another

- potential to kinetic - radiant to electric -
electric to heat - chemical to kinetic -
chemical to electrical
Energy before Energy after
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Kinetic Energy (KE) energy of motion

• KE ½ x Mass x Velocity2 ½ mV2
• KE depends on how heavy and how fast

Kinetic Molecular Theory the atoms and molecules
making up substances are in constant motion
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Potential Energy (PE) energy of position stored
energy of matter

• EXAMPLES
• stapler
• Rubberband

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• When Potential energy is released from matter it
  becomes kinetic energy

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Energy in Chemistrychemical energyheat energy
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Chemical Energy

• energy stored in bonds it is released as the
  result of a chemical reaction

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Heat Energy

• Heat energy that is in the process of flowing
  from warmer object to a cooler object
• Symbol for heat energy Q or q
• The amount of heat required to raise the temp. of
  1 gram of water 10C a calorie

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• Other Energy Units
• calorie, Calorie, BTUs
• 1 calorie 4.18 Joules
• 1 Calorie 1000 calories 1 kilocalorie
• NOTE When your body breaks down food, these
  reactions give off heat which is measured in
  calories (Thats why your food is labelled in
  calories)

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energy (heat) is given off exothermic EXO -
energy leaves system (exits)
Temperature of environment ? Temperature of
system ?
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energy (heat) is absorbed endothermicEndo -
Energy enters system (enter)
Temperature of environment ? Temperature of
system ?
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Energy of Universe is conserved

• Universe

Energy can move between the system and the
environment
Environment
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Calorimeter an insulated devise used for
measuring the amount of heat absorbed or released
during a chemical or physical change
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• universe is contained in Styrofoam cup
• environment is water
• system is whatever put in water

• Energy lost Energy gained
• Difficult to monitor system
• Easy to monitor environment (water)
• Energy lost/gained by environment
• Energy gained/lost by system

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The amount of heat transferred depends on 3 things

• Temperature change
• Mass of substance
• Specific Heat of substance

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Specific Heat
Found in Table B

• The amount of heat required to raise the temp of
  any given substance by 10C
• Symbol c
• Specific heat a physical constant
• unique for each pure substance

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Calculating Heat Transferred

• Simple system
• pure substance in single phase
• calculate heat gained or lost using

• Q mC?T

Q amount of heat transferred m mass of
substance C specific heat capacity of the
substance. ?T temperature change Tfinal
Tinitial
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Calorimetry

• 10 grams of NaOH is dissolved in 100 g of water
  the temperature of the water increases from 22?C
  to 30?C
• was dissolving process endothermic or exothermic
• how do you know?

Exothermic temperature of environment ?
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Dissolving

• Whats happening when NaOH dissolves?

molecules close together, not interacting
molecules pulled apart interacting with H2O
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Calorimetry

• Calculate energy released by NaOH as it dissolves
  in water
• Energy lost by NaOH Energy gained by water
  Easier to calculate from H2O perspective

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Calorimetry Q mC?T

• temperature of water increased from 22?C to 30?C
• 30?C -22?C 8?C ?T
• What mass to use? Well, temp change was for
  water, so want mass of water m 100 g
• Same goes for specific heat capacity calculate
  heat absorbed by water
• cH20 4.18J/g?

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Q mC?T

• Q (100 g)(4.18 J/g?)(8?C)
• Q 3344 Joules