THERMODYNAMICS
The study of HEAT and its transformation into
mechanical energy.
Greek Word:
"therme" - heat
"dynamis" - power
THERMODYNAMIC SYSTEMS
SYSTEM
SURROUNDINGS
BOUNDARY
The part of the
surroundings that
we chose to
study.
The rest of the
universe.
The surface
dividing the
system and
surroundings.
KINDS OF THERMODYNAMIC
SYSTEMS
OPEN
CLOSED
ISOLATED
Mass and Energy
can transfer
between the
system and the
surroundings.
Energy can
transfer between
the system and
the surroundings,
but not mass.
Neither Mass nor
Energy can
transfer between
the system and
the surroundings.
PROPERTIES OF A SYSTEM
A property is any quantity, which serves to describe a system.
INTENSIVE
EXTENSIVE
Is one which does not
depend on the size of the
system such as
temperature, pressure,
density, and velocity.
Is one which depends on
the size of the system such
as volume, momentum,
and kinetic energy.
TEMPERATURE
"hotness" or "coldness" of a body
a measure of the kinetic energy of the particles in a sample of
matter.
Absolute Zero is the temperature at which the molecules stop
moving. It is equivalent to 0 K.
Absolute Temperature is the temperature measured from
absolute zero.
TEMPERATURE CONVERSION
Relationship between Celsius and Kelvin
Relationship between Fahrenheit and Rankine
Relationship between Celsius and Fahrenheit
PROPERTIES OF A SUBSTANCE
PRESSURE
Is the force exerted per unit area.
DENSITY
Is the mass per unit volume.
SPECIFIC VOLUME
Is the volume per unit mass.
SPECIFIC WEIGHT
Is the weight per unit volume
SPECIFIC GRAVITY/
RELATIVE DENSITY
Is the ratio of the density of a certain
substance to the density.
PROPERTIES OF A SUBSTANCE
PRESSURE
continuous physical force exerted on or against an object by something in
contact with it.
SI Unit: Pascal (Pa) which is equivalent to Newton per square meter (N/m^2)
101,325 Pa = 101.325kPa
= 1 atm
= 760 torr
= 760mmHg
= 14.7 psi (pound force per square inch)
= 1.013x10^6 dyne/cm^2
= 1.013 bar
PROPERTIES OF A SUBSTANCE
DENSITY
p = Density (kg/m^3)
m = mass (kg)
V = Volume (m^3)
PROPERTIES OF A SUBSTANCE
SPECIFIC VOLUME
v = Specific Volume (m^3/kg)
p = Density (kg/m^3)
m = mass (kg)
V = Volume (m^3)
PROPERTIES OF A SUBSTANCE
SPECIFIC WEIGHT
W = Weight (N or kgm/s^2)
p = Density (kg/m^3)
m = mass (kg)
V = Volume (m^3)
g = acceleration due to gravity (9.8m/s^2)
PROPERTIES OF A SUBSTANCE
SPECIFIC GRAVITY/REALTIVE DENSITY
sg_substance = Specific Gravity of a substance with respect to reference (unitless)
p_substance = Density of the substance (kg/m^3)
p_H2O = Density of Water (1,000kg/m^3 or 1g/cm^3)
PROBLEM #1
The air pressure for a certain tire is 109 kPa.
What is this pressure in (a) atm (b) torr (c)
mmHg (d) pound per square inch - psi (e)
dyne/cm^2 (f) bar
PROBLEM #2
A certain rectangular material weighs 45g with
3cm height, 2.5cm width and 2cm length. Find
the density and its specific volume
counterpart (a) in g/cm^3 (b) in g/mL (c) in
kg/m^3 (d) in kg/L (e) in slug/ft^3 (f) in lbm/in^3
PROBLEM #3
A cylinder of plastic is 100 mm long, and 50
mm in diameter. It has a mass of 1 kg.
Determine its specific gravity and indicate
whether it would float or sink in water.
PROBLEM #4
A piece of unknown material has an intricate
shape. It has a mass of 126 g. You submerge it
to find it displaces 422 ml of water. What is the
specific gravity of the piece?
LAWS OF THERMODYNAMICS
0th Law
Equivalent Relation
1st Law
Conservation of Energy
2nd Law
State of Disorder
3rd Law
Absolute Zero
0TH LAW
EQUIVALENT RELATION
"If 2 objects are separately in thermal equilibrium
with third object, then the two objects are in
thermal equilibrium with each other."
THERMAL EQUILIBRIUM
This phenomenon is obtained if two objects with different
temperature is made to have contact, and reach a common
temperature.
In thermal equilibrium, the transfer of heat stopped.
THERMAL EXPANSION
As temperature increases, dimensions of objects increases.
ΔL = Change in Length (m)
α = Coefficient of Thermal Linear Expansion (/℃)
γ = Coefficient of Area Thermal Expansion (/℃)
β = Coefficient of Volume Thermal Expansion (/℃)
Lo = Original Length (m)
Ao = Original Surface Area (m^2)
Vo = Original Volume (m^3)
ΔT = Change in Temperature (℃)
Coefficient of Thermal Expansion on Various Materials
MATERIAL
Aluminum
Brass
Brick or Concrete
Copper
Glass, Pyrex
COEFFICIENT OF
THERMAL
EXPANSION (α: /℃)
MATERIAL
COEFFICIENT OF
THERMAL
EXPANSION (α: /℃)
Glass, Window
9.0 x 10^-6
Gold
14 x 10^-6
Ice
52 x 10^-6
Iron/Steel
12 x 10^-6
24 x 10^6
20 x 10^-6
12 x 10^-6
17 x 10^-6
3.3 x 10^-6
Coefficient of Thermal Expansion on Various Materials
MATERIAL
COEFFICIENT OF
THERMAL
EXPANSION (β: /℃)
MATERIAL
COEFFICIENT OF
THERMAL
EXPANSION (β: /℃)
Ethyl Alcohol
1.1 x 10^-4
Mercury
1.8 x 10^-4
Gasoline
9.5 x 10^-4
Water
2.1 x 10^-4
Glycerin
4.9 x 10^-4
Air
3.5 x 10^-3
PROBLEM #5
A surveyor uses a steel measuring tape that is exactly
50.000m long at a temperature of 20℃. (a) What is
its length on a hot summer day when the
temperature is 35℃. (b) The surveyor uses the
measuring tape to measure a distance when the
temperature is 35℃. The value he reads off the tape
is 35.794. What is the actual distance? Assume that
the tape is calibrated for use at 20℃.
PROBLEM #6
A glass flask with volume 200cm^3 is filled with to the
brim with mercury at 20℃. How much mercury
overflows when the temperature of the system is
raised to 100℃? The coefficient of linear expansion
of the glass is 0.40x10^-5 /K.
PROBLEM #7
The outer diameter of a glass jar and the inner
diameter of its iron lid are both 725mm at room
temperature (20.0℃). What will be the size of the
mismatch between the lid and the jar if the lid is
briefly held under hot water until its temperature
rises to 50.0℃, without changing the temperature of
the glass?
STRESS
STRAIN
characterizes the strength of the
forces causing thr deformation.
describes the resulting
deformation
σ = Tensional Stress (N/m^2)
F = Tension (N)
A = Area (m^2)
ε = Strain
ΔL = Change in Length (m)
Lo = Original Length (m)
MODULUS OF ELASTICITY
The proportionality constant of the stress and strain.
Y = Modulus of Elasticity
ΔL = Change in Length (m)
Lo = Original Length (m)
Modulus of Elasticity of Various Materials
MATERIAL
MODULUS OF
ELASTICITY (GPa)
MATERIAL
MODULUS OF
ELASTICITY (GPa)
Aluminum
70
Steel
200
Brass
90
Lead
16
Iron
210
Nickel
210
Copper
110
Concrete
40
Glass
60
THERMAL STRESS
The compression or expansion of material due to change in
temperature.
Y = Modulus of Elasticity
ΔT = Change in Temperature (℃)
α = Coefficient of Thermal Linear Expansion (/℃)
σ_thermal = Thermal Stress
PROBLEM #8
An aluminum cylinder 10cm long, with a crosssectional area of 20cm^2, is to be used as a spacer
between two steel walls. At 17.2℃ it just slips in
between the walls. When it warms to 22.3℃, calculate
the stress in the cylinder and the total force it exerts
on each wall, assuming that the walls are perfectly
rigid and a constant distance apart.
PROBLEM #9
A brass rod is 185cm long and 1.60cm in diameter.
What force must be applied to each end of the rod to
prevent it from contracting when it is cooled from
120.0℃ to 10.0℃?
PROBLEM #10
Steel train rails are laid in 12.0m long segments
placed end to end. The rails are laid on a winter day
when their temperature is -2.0℃. (a) How much space
must be left between adjacent rails if they are just to
touch on a summer day when their temperature is
33.0℃? (b) If the rails are originally laid in contact,
what is the stress in them on a summer day when
their temperature is 33.0℃?
Defined as the transfer of energy across the
boundary of a system due to a temperature
difference between system and surrounding.
Calorie (cal) - the amount of heat required to
raise 1℃ temperature of a 1 gram of water.
HEAT
British Thermal Unit (BTU) - is the quantity
of heat required to raise 1℉ of 1lb of water.
1cal = 4.186J
1BTU = 1,054J
SPECIFIC HEAT
Denoted as c
It is a measure of how thermally sensitive or insensitive a
substance is to the addition of energy.
Heat Capacity per unit mass.
Q = Heat
m = mass
c = specific heat
ΔT = Change in Temperature
MOLAR HEAT CAPACITY
Denoted as C
A proportionality constant between heat and
the temperature change.
Q = Heat
C = Molar Heat Capacity
ΔT = Change in Temperature
M = Molar Mass
n = number of moles
Specific Heats of materials (Constant Pressure)
MATERIAL
Specific Heat
(J/kg K)
Molar Mass,
M (kg/mol)
Aluminum
910
0.0270
Water
(liquid)
4160
0.018
Ice
2100
0.018
Copper
390
0.0635
Salt (NaCl)
879
0.0585
Iron
470
0.055
LATENT HEAT
The heat required per unit mass to change the Internal Energy
without changing the temperature in order to undergo phase
change.
n
io
tio
su
tio
n
bl
sa
in
en
at
nd
at
de
or
po
ap
si
n
ev
io
n
Q = Heat (J)
m = mass (kg)
L = Latent Heat (J/kg)
Latent Heat of Vaporization
Lv (H2O) = 2,256.7kJ/kg
co
Latent Heat of Sublimation
Ls (H2O) = 2838 kJ/kg
melting
freezing
Latent Heat of Fusion
Lf (H2O) = 333.5 kJ/kg
PROBLEM #11
A man working in the field drinks hot water out of an
aluminum cup. The cup has a mass of 0.120kg and is
initially at 20.0℃ when she pours in 0.300kg of water
initially at 70.0℃. What is the final temperature after
the water and the cup attain thermal equilibrium?
PROBLEM #12
An aluminum tea kettle with mass 1.50kg and
containing 1.80kg of water is placed on a stove. If no
heat is lost to surroundings, how much heat must be
added to raise the temperature from 20.0℃ to
85.0℃?
PROBLEM #13
A physics student wants to cool 0.25kg of water
initially at 25.0℃, by adding ice initially at -20℃. How
much ice should she add so that the final
temperature will be 0℃ with all the ice melted if the
heat capacity of the container may be neglected.
PROBLEM #14
A heavy copper pot of mass 2.0kg (including the
copper lid) is at a temperature of 150℃. You pour
0.10kg of water at 25℃ into the pot, then quickly
close the lid of the pot so that no steam can escape.
Find the final temperature of the pot and its
contents, and determine the phase (liquid or gas) of
the water. Assume that no heat is lost to the
surroundings.