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Thermodynamics
Thermodynamics
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Temperature
Particles
Pressure, volume and temperature
Energy and Power
Heat transfer
Measuring Temperature
Specific heat capacity
Latent heat
ENERGY
Energy (Joule)
• Energy can be transferred or transformed
• kinetic
• potential (chemical, electrical, gravitational,
elastic)
• radiant (sound, light and other
electromagnetic waves)
• internal (heat/thermal energy)
TEMPERATURE
Temperature
The temperature of an object is given by the
average kinetic energy of its particles.
2. Measuring temperature
Which thermometers use thermal expansion as
their thermodynamic property?
a) liquid in glass
b) thermistor
c) constant volume gas thermometer
d) thermocouple
a) liquid in glass
Temperature Scales
use a thermodynamic property
scales calibrated at 2 fixed points (often melting
ice and boiling water
INTERNAL ENERGY
Internal Energy
The internal energy of an object is the total
kinetic and potential energies of the particles.
U = EK +EP
5. Internal Energy
During a change of state from solid to liquid at
the melting point:
a) the temperature of the substance stays the
same
b) the internal energy of the substance stays the
same
c) the kinetic energy of the particles stays the
same
Internal Energy
Internal Energy
= potential energy of particles
+ kinetic energy of particles
U = PE + KE
Heat  increases internal energy
a) the temperature of the
substance stays the same
and
c) the average kinetic energy of
the particles stays the same
Which liquid has more internal energy?
cup of hot tea 80oC
water in swimming pool 25oC
THERMAL EQUILIBRIUM
Temperature
average kinetic energy of a particle
different temperatures  heat transferred
until thermal equilibrium
States of matter
1. Thermal Equilibrium
When two objects are in thermal equilibrium:
a) their particles are moving at the same speed
b) they each contain the same amount of
internal energy
c) the average kinetic energy of the particles in
each object is the same
c) the average kinetic energy of
the particles in each object is the
same
Heat transfer
Which ice cube will melt first?
GASES
The Ideal Gas
all collisions between atoms or molecules are
perfectly elastic
no intermolecular attractive forces
Image: http://kaffee.50webs.com/Science/activities/Chem/Activity.Gas_Laws.PSet1.html
Charles’ Law
Charles’ Law: the volume of a gas is
proportional to the Kelvin temperature at
constant pressure
V = kT
V1 = T1
V2 T2
Absolute zero
Absolute zero is the temperature at which the
particles of a substance have no kinetic
energy. This occurs at -273oC.
Kelvin temperature scale
The Kelvin scale of temperature is defined by
absolute zero and is designed so that 1 Kelvin
= 1 oC. This gives absolute zero (0K) as -273.15
oC.
Example: Calculate the volume at 75ºC of of a gas sample
that at 40ºC occupies a volume of 2.32 dm3
Convert temperatures to Kelvin. 40C = 313K
75C = 348K
2.32 dm3 = 313 K
V2
348K
(313K)( V2) = (2.32 dm3) (348K)
V2 = 2.58dm3
Heat Transfer
How is heat transferred?
• Conduction
• Convection
• Radiation
specific heat capacity
How much energy is needed to
increase temperature?
Heat capacity
• Describe what happens to the temperature of
liquid coffee at 90°C when it is poured into a
cup at room temperature.
• Which direction does heat flow?
Image:http://en.wikipedia.org/wiki/Coffee
Heat capacity
• The heat capacity of an object is the energy
required to raise its temperature by 1°C
Image: http://en.wikipedia.org/wiki/Milk
Heating water
It takes 4180J of heat energy to
increase the temperature of 1kg
of water by 1°C.
a) how much heat is needed for
0.5kg by 1°C?
b) how much heat is needed for
1kg from 20 to 50C?
c) how much heat for 5kg from 20
to 100C?
specific heat capacity
Heat energy = mass of × specific heat × temperature
substance
capacity
change
E
=
m
×
c
×
∆T
(J)
(kg)
(J/kg/°C)
(°C)
The specific heat capacity is the amount of heat
needed to raise the temperature of a mass of one
kilogram of a substance by 1 degree Celcius.
Coffee example
6. Specific Heat Capacity
Specific heat capacity of water is 4180J/kg/K
This means 4180J of energy is needed to
a) increase the temperature of 10g of water from
20 to 30C
b) increase the temperature of 1 litre of water
from 20 to 21C
c) increase the temperature of 0.1kg of water
from 40 to 50C
b) increase the temperature of 1
litre of water from 20 to 21C
and
c) increase the temperature of
0.1kg of water from 40 to 50C
Specific Heat Capacity
E = mcΔT
shc found from 'the electrical method' or 'the
method of mixtures'.
Latent heat
Latent Heat
Latent heat of fusion: energy needed to melt a
solid without a temperature rise
Latent heat of vaporization: energy needed to
boil a liquid without a temperature rise.
Energy = mass × spedific latent heat
E = mL
Ideal gases
3. Temperature and Pressure
The temperature of an ideal gas (in Kelvin) is
proportional to its pressure so
a) at absolute zero the pressure is zero
b) at absolute zero the particles have no kinetic
energy
c) below absolute zero the pressure is negative
a) at absolute zero the pressure
is zero
and
b) at absolute zero the
particles have no kinetic
Pressure
Gas pressure due to collisions of gas particles
with container walls.
Higher temperature > more collisions, more KE
Unit of pressure: Pascal 1 Pa = 1 N/m2
4. Pressure, Volume and
Temperature
When the pressure of an ideal gas is doubled
a) the volume is half if the temperature is kept
constant
b) the volume is double if the temperature is
kept constant
c) the temperature is double if the volume is
kept constant
a) the volume is half if the
temperature is kept constant
and
c) the temperature is double
Pressure, Volume and Temperature
P1V1 = P2V2 for a fixed mass of gas
T1
T2