Transcript Energy (download)

Energy
Temperature
Energy
Heat
Learning objectives
• Perform conversions among different
scales of temperature
• Define energy and distinguish among types
of energy
• Perform simple energy calculations using
different energy units
• Apply specific heat concept to heat
calculations
• Determine caloric contents of food stuffs
based on composition of macronutrients
Temperature is the
measure of hotness
•
A fundamental unit. There
are three(3) temperature
scales
BPH20
FPH2O
Difference
(1) Fahrenheit (F)
212°
32°
180°
(2) Celsius (centigrade) (C)
100°
0°
100°
(3) Kelvin (K)
373
273
100
Temperature
conversions
• Conversion:
Kelvin to Celsius (K -> ºC)
ºC = K - 273
Celsius to Kelvin (ºC -> K)
K = ºC +
273
Celsius to Fahrenheit (ºC -> ºF)
i multiply ºC x 9/5
ii Add ºC x 9/5 + 32
Fahrenheit to Celsius (ºF -> ºC)
i add ºF - 32
ii multiply (ºF - 32) x 5/9
Working with temperature
conversions
Heat and chemical
reactions
• The burning candle is
a chemical reaction
• It releases energy
that heats the air
molecules
• Heat is flow of energy
from a higher to a
lower temperature
Energy from chemical
reactions performs work
• Energy is capacity to do work
• In what way is a human like a
car?
• Both burn fuel to run
• Humans burn glucose
• C6H12O6 + O2 = CO2 + H2O
• Cars burn petrol
• C8H18 + O2 = CO2 + H2O
Energy comes in many
forms
• Kinetic energy is energy due to motion
•
•
•
•
Heat
Rotation
Vibration
Translation
• Potential energy is energy due to position
or state
•
•
•
•
Height
Chemical
Electrical
Coiled spring
Energy can be
converted
• Processes convert
energy from one form
to another
• Falling down stairs
• (potential → kinetic
→ pain)
• Chemical reaction
• (potential →
heat/light)
• Battery
• (potential →
electrical)
• Engine
• (potential → heat →
kinetic)
But it never goes away
• Energy is conserved in any
process
• None is lost
• None is gained
• Law of Conservation of Energy:
Energy is neither created nor
destroyed in a chemical
reaction
Perpetual motion is a thing
of smoke and mirrors
• Visit the
museum of
unworkable
machines to
view a history of
conmen and
failure
Measuring energy: calories,
Calories and joules
• calorie is energy
required to raise
temperature of 1 g of
water 1 degree C
• Calorie is the food
version = 1,000 cal
• Raises temperature of
1 pint of water 3.8ºF
• Joule is SI unit derived
from mechanical work:
work done when force
of 1 Newton is applied
for 1 meter
1 cal = 4.18 J
Common energy
conversions
• 10 g of octane is burnt to produce
8500 J. How much is that in
calories?
• 1 cal = 4.18 J