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Food and EnergyThe Basics of Heat
Transfer
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The Flow of Energy
Thermochemistry - concerned with heat changes that occur during chemical reactions
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Cranking up the Heat: Basic ThermodynamicsEnergy - capacity of an object
to do work or produce heat
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Kinetic EnergyThe energy an object has due
to its motion
Potential EnergyStored energyEnergy of position
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External EnergyThe energy applied to an object by another source
Internal EnergyEnergy within an object
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Energy in the universe is constant, though it changes forms.
Law of Conservation of energyLaw of Conservation of energy – energy can neither be created nor destroyed
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Forms of Energy Mechanical Chemical Electrical Nuclear Radiant
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Mechanical Energy The total kinetic and potential energy of a
system Examples- lifting weights, chewing food,
opening the refrigerator
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Chemical Energy The energy resulting from the forming or
breaking of bonds in a chemical reaction Endothermic reaction- A reaction whose
products have less total heat than the reactants
Exothermic reaction- where energy is released during the reaction
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Electrical Energy Energy that is produced by the movement of
electrons Example- electricity
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Radiant Energy Energy transmitted in the form of waves through
space or some medium. Also known as the electromagnetic spectrum Examples- light, radio waves, UV waves,
microwaves A microwave oven has a magnetron, which is an
electron tube that converts electrical energy into microwaves
The more water in food, the faster a microwave oven will cook it since the energy agitates water molecules
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Nuclear Energy Energy from the splitting or combining of
atoms of certain elements that then gives off radiation
Examples- X-rays, nuclear power plants, irradiation
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Heat vs. TemperatureTemperature and heat are not the same thing.
Temperature- the measure of the average kinetic energy of a group of individual molecules
Heat- describes amount of energy transferred from one object to another caused by a temperature difference between the two bodies
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Describing Energy ChangesHeat flow is from the warmer object to
the cooler object
Heat Flow
Heat Flow
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Describing Energy ChangesHot day 50°C = 122°F
Beans lost energy, it was transferred to its surroundings. This change of energy would be negative change = ∆
Energy transferred from fire to beans. Change in energy for beans would be positive.
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Endothermic reactions – absorbs heat, ∆H is positive, the surroundings cool down
Exothermic reactions – releases heat, ∆H is negative, the surroundings heat up
Heat
Surroundings
Heat
Surroundings
Describing Energy Changes
Feels cold to the touch
Feels warm to the touch
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Heat Transfer Three methods of heat transfer Conduction- the transfer of heat through
matter from particle to particle collisions Convection- the transfer of heat by the
motion of fluids, such as water and air Radiation- the transfer of heat by
electromagnetic waves
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Units used to describe Energy:
calorie – called “little calorie” – (cal)
kilocalorie – called “Big calorie”- (CAL) 1000 calories – same as a food calorie
Joule – the SI unit of heat - (J)
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CONVERSION FACTOR
1 cal = 4.184 joules
1 cal 4.184 J
4.184 J 1 cal
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Energy Flow and Phase Changes Fusion- The movement from a solid to a
liquid phase, aka melting Crystallization- The movement from a liquid
to a solid phase, aka freezing Latent heat of Fusion- The energy needed to
melt or freeze a substance
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Energy Flow and Phase Changes Evaporation or Vaporization- The phase
change from the liquid to the gaseous phase Condensation or Liquefaction- The change of
a gas to a liquid Latent heat of vaporization- The amount of
heat needed to either evaporate or condense a substance
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Energy Flow and Phase Changes Latent heat- The energy required to complete
a phase change without a change in temperature
Deposition- The changing of a substance directly from a gas to a solid, ex. Frost forming on a window
Sublimation- The changing of a substance directly from a solid to a gas
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Phase Change Diagram