Transcript Chapter 5 Notes

Food and Energy
The Basics of Heat
Transfer
The Flow of Energy
Thermochemistry - concerned
with heat changes that occur
during chemical reactions
Cranking up the Heat:
Basic Thermodynamics
Energy - capacity of an object
to do work or produce heat
Kinetic Energy

The energy an object has due to its
motion
Potential Energy
Stored energy
 Energy of position
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External Energy

The energy applied to an object by
another source
Internal Energy

Energy within an object
Energy in the universe
is constant, though it
changes forms.
Law of Conservation of energy –
energy can neither be created nor
destroyed
Forms of Energy
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Mechanical
Chemical
Electrical
Nuclear
Radiant
Mechanical Energy
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The total kinetic and potential energy of a
system
Examples- lifting weights, chewing food,
opening the refrigerator
Chemical Energy

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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
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Energy that is produced by the movement of
electrons
Example- electricity
Radiant Energy
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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
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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. Temperature
Temperature and heat are not the same thing.
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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 Changes
Heat flow is from the warmer object to
the cooler object
Heat Flow
Heat Flow
Describing Energy Changes
Hot day 50°C = 122°F
Energy transferred from fire to beans.
Change in energy for beans would be
positive.
Beans lost energy, it was transferred to its surroundings. This
change of energy would be negative
change = ∆
Describing Energy Changes
Endothermic reactions – absorbs heat, ∆H is
positive, the surroundings cool down
Surroundings
Feels cold to
the touch
Heat
Exothermic reactions – releases heat, ∆H is
negative, the surroundings heat up
Surroundings
Heat
Feels warm to
the touch
Heat Transfer
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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)
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kilocalorie – called “Big calorie”- (CAL)
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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
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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
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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
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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