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Food and EnergyThe Basics of Heat
Transfer
The Flow of Energy
Thermochemistry - concerned with heat changes that occur during chemical reactions
Cranking up the Heat: Basic ThermodynamicsEnergy - capacity of an object
to do work or produce heat
Kinetic EnergyThe energy an object has due
to its motion
Potential EnergyStored energyEnergy of position
External EnergyThe energy applied to an object by another source
Internal EnergyEnergy within an object
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
Forms of Energy Mechanical Chemical Electrical Nuclear Radiant
Mechanical Energy The total kinetic and potential energy of a
system Examples- lifting weights, chewing food,
opening the refrigerator
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
Electrical Energy Energy that is produced by the movement of
electrons Example- electricity
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
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
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
Describing Energy ChangesHeat flow is from the warmer object to
the cooler object
Heat Flow
Heat Flow
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.
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
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
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)
CONVERSION FACTOR
1 cal = 4.184 joules
1 cal 4.184 J
4.184 J 1 cal
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
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
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
Phase Change Diagram