Thermodynamics
Matter on a micro-scale
As you learned in chemistry, all matter is made up of
tiny particles called atoms and molecules and
these particles are in constant motion
Simulation
Since molecules and atoms have mass and are in
motion, they also have kinetic energy.
Temperature vs. Thermal Energy
Thermal energy is the sum total Kinetic energy of the
particles of a substance
Temperature is a measure of the AVERAGE KINETIC
ENERGY of a substance’s molecules.
Is it possible to have a very low temperature and a
very high amount of thermal energy?
Watch This
Temperature Scales
We are used to using the Fahrenheit Scale (°F) in the
US, but in this class we will use either Celsius
(°C)or Kelvin (K) temperature Scales.
Celsius Scale
On the Celsius (sometimes called centigrade) scale,
the freezing point of water is 0°C and the boiling
point of water is 100°C.
Therefore, the change from freezing to boiling is 100
units
On the Fahrenheit scale the change from freezing to
boiling is 180 units and therefore a Fahrenheit degree is
smaller than a Celsius degree.
Kelvin Scale
The Kelvin Scale is based on a theoretical
temperature called absolute zero
Absolute zero is the temperature at which all molecular
motion STOPS
Absolute Zero Video
A Kelvin unit is equal in size to a Celsius degree
(difference from freezing to boiling of water is 100
units)
To calculate Kelvin temperature
K = °C + 273
Heat
Heat is the transfer of energy
Heat ALWAYS flows FROM HIGH TO LOW
There are three ways heat is transferred.
1. Conduction – transfer of heat through contact
2. Convection- transfer of heat through the motion of a
fluid (such as air)
3. Radiation – transfer of heat through electromagnetic
waves (microwaves oven)
Heat Transfer
And the Laws of Thermodynamics
Zeroth Law
If object A is in thermal equilibrium with object B
and Object B is in thermal equilibrium with object
C, then Objects A and C are in thermal equilibrium
with each other.
First Law
When heat is transferred from or to a system work is
done on or by the system
Second Law
Heat ALWAYS moves from area of greater thermal
energy to area of lower thermal energy unless work is
performed on the system. The total entropy
(disorder) of the universe increases.
Entropy
Entropy is a measure of the amount of disorder in a
system. With every thermodynamic process, entropy
is either constant, or increases. It will Never naturally
decrease.
Heat Transfer Equation
Specific Heat (c)  the amount of heat energy
needed to raise or lower the temperature of 1 kg
of a substance by 1 K (1°C)
Specific heat is measured in J/kg∙K
Heat Transfer Equation
The equation for calculating the amount of heat
gained or lost is as follows:
Q = mcΔT
Q  heat transferred (positive Q means energy gained, negative Q means
energy is lost)
M  mass measured in kilograms
C  specific heat of the material
ΔT  the change in temperature (in Kelvins)
• How much energy is required to bring 1 L (hint: 1L
of water = 1Kg of water) of water from 0°C to
100°C? (specific heat of water is 4180 J/kg∙K)
• 356.0 kg of an unknown substance is heated from
25 K to 398°C. If this process required 6589 J of
heat, what is the specific heat of the unknown
substance?
• You add 12000 J of heat to a 25 kg sample of copper
(specific heat of copper is 380 J/kg∙K). If the final
temperature of the copper is 480 K, what was its
initial temperature in Celsius?