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Kinetic Molecular Theory
the theory that describes the motion of molecules or atoms in a substance in terms of kinetic energy
Caloric (old, debunked concept)
a massless fluid that was thought to be responsible for heat transfer between objects
how do particles behave in a solid
held in fixed positions by attraction, vibrate due to their kinetic energy
how do particles behave in a liquid
particles have more kinetic energy than a solid, and move rapidly and from place to place, although still staying not far from each other
how do particles behave in a gas
particles have more kinetic energy than other states, vibrate and move much farther and much more rapidly
Thermal Energy
total kinetic and potential energy posessed by the atoms/molecules of a substance
⇨ unit is Joules (J)
Thermal Energy depends on:
mass, temperature, nature, and state
Thermal Energy when an object warms up vs cools down
Warms up = absorbs
Cools down = released
Heat
used as a verb, the transfer of thermal energy from warm ➙ cold
Temperature
a measure of the average kinetic energy of the particles in a substance
⇨ temperature increases if the motion of the particles increases (and vice versa)
Temperature is measured using:
mercury or alcohol thermometer
How does a thermometer work? (placed in a warmer substance)
• particles of the substance bump into the glass of the thermometer
• particles of the glass collide with the particles of mercury or alcohol
• mercury/alcohol particles spread out and take up more space, rising in the tube
how does a thermometer work? (placed in a colder substance)
• glass particles collide with slow substance particles, transferring their energy to them
• this causes the glass particles to slow down
• in turn, the particles of the mercury/alcohol collide with the glass particles, and slow down as well
• these particles now slow down and take up less space, sinking in the tube
What is 0 Kelvin?
-273°C
⇨ point at which there is virtually no motion in the particles, absolute zero
Why do 2 iron nails of different mass but same temperature have different thermal energies?
☆ Temperature is a measure of the average kinetic energy of the particles. The particles in both nails are moving at the same speeds, therefore have the same temperature.
☆ Thermal energy is the sum of energy from all particles. The nail with more mass has more particles, and therefore a larger sum of energy than the one with a smaller mass.
3 methods of transferring thermal energy
1. Conduction
2. Convection
3. Radiation
Conduction
occurs through collision of atoms, only occurs if objects are in physical contact
Convection
⇨ occurs through a fluid when colder, denser fluid falls and pushes up warmer, less dense fluid
⇨ creates a convection current
⇨ spreads thermal energy evenly throughout the fluid
How are ocean breezes created
cool air from over the water moves onto the land to replace the rising warm air, creating an ocean breeze during the day
Radiation
transfer of thermal energy as electromagnetic waves, does not require collision or movement of particles (ex: the sun)
Thermal Conductor
a material that conducts thermal energy well
Thermal Insulator
a material that conducts thermal energy poorly
What is the BEST thermal insulator? Why?
a vacuum! it contains none or very few particles, meaning thermal energy cannot be transferred by conduction or convection
How do thermos bottles insulate so well?
❄ has a vacuum between an inner flask and an outer flask, minimizing conduction and convection
❄ the inner flask is coated in a mirror-like layer, reflecting any thermal energy that is transferred by radiation
Specific Heat Capacity (c)
amount of energy required to raise 1 kg of a substance's temperature by 1°C
⇨ unit is J/kg × °C
(also represents how much thermal energy is released when a substance cools by 1°C)
Specific Heat Capacity of water
4180 J/kg × °C
Quantity of Heat (Q)
total amount of thermal energy transferred from one object to another
⇨ Q = mcΔT
Principle of Thermal Energy Exchange
when thermal energy is transferred from a warmer object to a colder object, the amount of thermal energy released by the warmer object is equal to the amount of thermal energy absorbed by the colder object
Exceptions to the principle of thermal energy exchange
In most circumstances, some thermal energy will be released into the surrounding environment (ex: air, container, surfaces)
Thermal expansion
expansion of a substance as it warms up
Thermal contraction
contraction of a substance when it cools down
Explain thermal expansion
As a substance absorbs thermal energy, some of this energy is transformed into kinetic energy. This causes the particles to spread out and increase in volume.
what do the flat lines on a heating or cooling graph represent?
constant temperature during a change of state
why is temperature constant during a change of state?
Yes, there is a change in thermal energy, but that change results in a change in potential energy in the particles. Since temperature is a measure of the average kinetic energy, it remains constant through this process.
Latent Heat (Qf and Qv)
the total thermal energy absorbed or released when a substance changes state
⇨ Qf = mLf
⇨ Qv = mLv
Specific Latent Heat of Fusion (Lf)
the amount of thermal energy required to melt or freeze 1 kg of a substance
Specific Latent Heat of Vaporization (Lv)
the amount of thermal energy required to evaporate or condense 1 kg of a substance
Unit for specific latent heat (L)
J/kg
Most solids ____ in their respective liquids. Why?
sink. This occurs because the particles of the solid are more closely packed than the particles of the liquid, making the solid denser
Why is water a special liquid compared to other substances?
Ice floats on liquid water, as ice is less dense than water.
Why is ice less dense than water? What is another side-effect of this?
❄ Because of water molecules' chemical structure
❄ At warmer temperatures (above 4°C) they are relatively disorganized. As they get colder, the molecules move slowly enough for the forces of attraction to place them into an organized structure.
❄ This takes up more space, making ice less dense and also leading to expansion as water freezes
❄ This expansion causes problems like burst pipes in the winter when pipes freeze
Electrical Heating Systems
uses electric currents through metal wires to produce thermal energy for heating
Forced-Air Heating System
uses a furnace to warm air and then passes the air through ducts and then vents
Hot Water Heating System
uses a boiler to heat water that is pumped through pipes and then radiators
Explain the Conventional Cooling System (parts and steps)
❄ Expansion Valve: the refrigerant enters the systems as a liquid and drops in pressure, cools, and turns into a gas (due to the sudden drop in pressure).
❄ Evaporator: the cool refrigerant gas flows through the evaporator coil, where it absorbs heat from the air inside. This heat absorption causes the refrigerant to evaporate fully into gas.
❄ Compressor: the warm refrigerant gas is then drawn into the compressor, where it gets squeezed. This compression raises both the temperature and pressure of the gas, turning it into a hot, high-pressure gas.
❄ Condensor: the hot, high-pressure gas then moves into the condenser coils where the refrigerant releases its heat into the surrounding air/atmosphere, cooling down and turning back into a liquid in the process.
❄ The liquid refrigerant then returns to the expansion valve, and the cycle repeats.
[ better explanation: https://youtu.be/EIP3pSio7-M?si=I-MOd-pUV6mQ_SXK ]
Geothermal System
transfers thermal energy in (heating) or out (cooling) from under earth's surface into a building (uses a liquid)
