Transcript Thermodynamics!!!

Thermodynamics!
Heat
 Heat is the transfer of
energy between two
objects.
 It is an electromagnetic
wave when in the
radiant form; otherwise
the vibrations of the
atoms and molecules
transfer heat as
internal energy.
Units of Heat
 The official SI unit is the Joule (J)
 Heat calorie (cal) = 4.186 J
 Kilocalorie (kcal) = 4186 J
 Food Calorie (C) = 4186 J
 British thermal unit (btu) = 1055 J
 Therm = 105,500,000 J
Temperature and Energy
 When objects receive or lose heat their
temperature changes and the internal energy
changes.
 Types of Internal Energy
 A) Translational
 B) Rotational
 C) Vibrational
Movement of Heat
 First thing you need to remember
is that there is NO such thing as
COLD, only a lack of heat
 Temperature is the measurement
of the average kinetic energy of
the molecules of a substance
 Heat always moves from “warm
to cold” meaning from something
with a higher temperature to
something with a lower
temperature
Thermal Equilibrium
 When two or more substances of different
temperatures are mixed or combined, the
heat from the warmer object will move to
the cooler object until the temperature
of both are balanced.
 The temperature at Thermal Equilibrium
will be lower than the initial of the
warmer object and higher than the initial
of the cooler object.
Temperature Conversions
 There are three equations for temperature
conversions that are important to know in
this section.
 TF = 9/5 Tc + 32.0
 Tc = 5/9(TF - 32.0)
 TK = TC + 273.15
Independent Practice

°C to °F
1. 27 °C
2. 87 °C
3. 2 °C
4. -10. °C
5. 12 °C

°F to °C
1. 50 °F
2. 25 °F
3. 88 °F
4. -5 °F
5. 0 °F

°C or °F to K
1. 10 °C
2. 10. °F
3. 25 °F
4. 50 °C
5. 75 °C
Answers
 °C to °F
1. 27 °C =
81 °F
2. 87 °C =
190 °F
3. 2 °C =
40 °F
4. -10. °C =
14 °F
5. 12 °C =
54 °F
 °F to °C
1. 50 °F =
10 °C
2. 25 °F = 3.9 °C
3. 88 °F =
31 °C
4. -5 °F =
-20 °C
5. 0 °F =
-20 °C
 °C or °F to K
1. 10 °C =
300 K
2. 10. °F =
260 K
3. 25 °F =
270 K
4. 50 °C =
300 K
5. 75 °C =
350 K
Heat Transfer
Convection
 The transfer of heat
through the
movement of
liquids and gases
 Ex: turbulence,
climate changes,
wind, boiling water
Hot water rises, cools, and falls.
Heated air rises, cools, then falls.
Air near heater is replaced by
cooler air, and the cycle repeats.
Ocean Convection Currents
Thermal Image
Ocean Convection Currents
Sea Breeze


Solar radiation reaching
the earth causes the
land to warm which in
turn warms the air
(atmosphere) above the
land.
Due to greater density,
land masses warm faster
than bodies of water.
Air above the land
warms faster, rises, and
pulls cooler air from
over water onto the
land, creating what is
called an on-shore (sea)
breeze.
Offshore Breeze

When the water adjacent to a land mass is warmer, air
above the water warms faster, rises, and pulls air above
the land off the shore. This is called an off-shore
breeze.
Conduction
 The transfer of heat
through touch
(direct contact)
Radiation
 The transfer of heat
through
electromagnetic waves
Calculating the Sun's Temperature
What is the Sun's temperature? (Assume the Sun's emissivity (e)
is 1.)
Distance from Sun to Earth: R = 1.5 x 1011 m
Area of sphere of radius R = 4πR2 H = 1000 x 4πR2 = 2.83 x
1026 J/s
Radius of the Sun = r = 6.9 x 108 m
Surface area of the Sun = A = 4πr2 = 5.98 x 1018 m2
esAT4 = H s = 5.67 x 10-8 SI units T = [H/(esA)]1/4 = 5375 K
http://sol.sci.uop.edu/~jfalward/heattransfer/heattransfer.html
Specific Heat
 Every substance has a unique specific
heat capacity (Cp)
 The specific heat is the amount of
energy required to raise 1 g of a
substance 1 °C
 The amount of energy to raise or lower
the temperature of a substance
 Q = mCpΔT
Latent Heat
 The heat required during a phase
change.
 Q = mLf/v (fusion or vaporization)
Thermodynmaics
 the study of heat and how it is used to
do work.
 The internal energy of a substance can
be used to do work.
 Heat and work can be transferred to or
from a system.
Work
 Specifically, we are going to look at the
work done by a gas.
 W = -PΔV
 P – Pressure (Pa)
 ΔV – change in volume (m3)
 When work is done by (does, expand) the
system the work is negative (losing energy).
 When work is done on (compressed) a
system work is positive (gaining energy).
The First Law of Thermodynamics
U=Q+W
 U – Internal Energy
 Q – Heat
 W – Work
 Unit for all is J
 Energy is conserved
 When heat is added, Q is positive
 When heat is removed, Q is negative
Types of Thermodynamic Processes
 Isovolumetric – the volume of a system
remains constant
 If ΔV = 0, then W = 0
 If W = 0, then U = Q
Types of Thermodynamic Processes
 Isothermal – The temperature of the
system remains constant
 ΔU = 0
 Adiabatic – no energy is transferred to
or from the system (happens very
quickly)
 Q = 0 , ΔU = W
The Second Law of Thermodynamics
 No cyclic process that converts heat into
work is 100% possible.
 When energy is used to do work, some
energy will always be turned into
unusable heat that is lost to the universe
 Entropy – the measure of randomness or
disorder of a system (S)
 The entropy of the universe is always
increasing.