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Topic 4
Transformations and Conservation of
Energy
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Energy- The ability to do work.
• Different forms include chemical, electrical, thermal, potential, and kinetic.
• Potential- stored energy available to do work.
• Kinetic- energy in motion.
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Conservation of Energy• The law of conservation of
energy states that energy cannot be created or destroyed, but can change forms. These are transformations.
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Energy Transformations
• Energy can be transformed into other forms.
• Example: In a solar panel the Sun (electromagnetic) is converted into into electrical energy.
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Transformations
generator (electrical)
Battery(chemical)
defroster
(thermal)
ignition
(electrical)
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Open and Closed Systems
• A closed system would not permit loss of matter outside the system. Energy is conserved. Example: insulation
• In an open system, energy is lost. Energy is not conserved.
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Phase Changes• In a phase change energy is
absorbed into a system. For example, ice absorbs energy, increasing the motion of the molecules. Ice becomes a liquid. The energy required is called heat of fusion.
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Phase Changes• When liquid water absorbs
energy, the molecules move faster, and the temperature of the water increases. The energy needed to raise 1 g 1°C is called the specific heat.
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Phase Changes• When the energy of the
molecules becomes high enough the vapor pressure exceeds the atmospheric pressure, and the liquid boils. This energy is called heat of vaporization.
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Energy Units• calorie- the amount of energy it
takes to raise 1 gram of water 1 degree Celsius.
• 1,000 calories = 1 Calorie• 1 calorie = 4.2 Joules• 1 kilojoule = 1,000 Joules
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Heat of Fusion• It takes 334 Joules to change one
gram of ice to one gram of water.
• How many joules does it take to change 10 grams of ice to 10 grams of water?
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Specific Heat• It takes 4.2 joules to raise one gram
of water 1 degree celsius.
• How many joules does it take to raise 10 grams of water 20 degrees celsius?
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Heat of Vaporization• It takes 2,260 joules of energy to
change 1 gram of water from a liquid to a gas.
• How many joules would it take to change 30 grams of liquid water to a gas?
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Total Energy
• You can add the heat of fusion, specific heat and heat of vaporization to get the total energy required to change a solid to a gas.
• You will find the heat required to change water from a solid to a gas in class.
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The End