Thermodynamics Review
Definition: The branch of physical science that deals with the relations between heat and other forms of
energy (such as mechanical, electrical, or chemical energy), and, by extension, of the relationships
between all forms of energy.
Laws of Thermodynamics
1. The zeroth law of thermodynamics states that if two thermodynamic systems are each
in thermal equilibrium with a third, then they are in thermal equilibrium with each other.
2. The 1st Law of Thermodynamics, also known as Law of Conservation of Energy, states that
energy cannot be created or destroyed in a chemical reaction.
3. The 2nd Law of Thermodynamics state that thermal energy flows from hot to cold. (Entropy is
the measure of how evenly distributed heat is with a system.)
4. The 3rd Law of Thermodynamics states that states that the entropy of a system approaches a
constant value as the temperature approaches absolute zero.
Temperature Scales
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Scale
Freezing Point of Water
Boiling Point of Water
Celsius
Fahrenheit
Kelvin
0°C
32°F
273°K
100°C
212°F
373°K
Matter is made up of molecules in motion (kinetic energy)
An increase in temperature increases motion.
A decrease in temperature decreases motion
Absolute zero occurs when all kinetic energy is removed from an object (Ok = -273 °C)
Thermodynamic Equilibrium is obtained when touching objects within a system reach the same
temperature. When equilibrium is reached, the system loses its ability to do work.
Types of Energy Transfer
1. Conduction – The transfer of thermal energy within an object between objects from molecule to
molecule.
2. Convection- The transfer of thermal energy by movement of a fluid (liquid or gas).
3. Radiation- The process by which energy is transmitted through a medium, including empty
space, such as electromagnetic waves.
Types of Energy
1. Kinetic Energy – The energy of motion
2. Potential Energy – The energy of the amount of work an object does
3. Thermal Energy- The energy of an object’s amount of kinetic energy of its molecules
Variables
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P = rate of energy transfer (measured in watts)
Q = energy transfer (measured in Joules)
∆t = change in time (measured in seconds)
K = thermal conductivity (measured in Joules/(seconds × meters × °C))
A = area of thermal conductivity (usually measured in meters, but depends on the problem)
L = thickness of material (usually measured in meters, but depends on the problem)
∆T = difference in temperature (measured in Celsius or Kelvin, usually)
U = U-Value ; coefficient of heat conductivity ; The measure of a material’s ability to conduct
heat (watts/square metre per degree Kelvin)
R = R-Value ; Thermal resistance of a material ; The measure of a material’s ability to resist heat
(kelvin/kilograms)
e = emissivty constant
σ = Stefan’s constant : 5.6696 × 10-8 (watts/ (m2 × K4)
Equations
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Q = M × C × ∆T
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Qgain = Qloss
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P = Q/∆t
P = (K × A × ∆T)/L
U = P/(A × ∆T)
R = 1/U
Bulk R-Value = R-Value Object 1 + R-Value Object 2 + R-Value Object 3…
**EACH EQUATION CAN BE MANIPULATED BASED ON WHAT THE PROBLEM IS ASKING FOR**