Thermal Properties Flashcards
What are the three states of matter?
Solid, Liquid, Gas
How are molecules arranged in solids, liquids, and gases?
- Solids: Regular arrangement, closely packed
- Liquids: Irregular arrangement, close together
- Gases: Irregular arrangement, far apart
How does intermolecular distance change across states of matter?
- Solids: Molecules are closely packed
- Liquids: Molecules are close together
- Gases: Molecules are far apart
How does intermolecular force compare in different states?
- Solids: Very strong
- Liquids: Strong
- Gases: Very weak
Which states of matter are compressible?
Only gases are compressible; solids and liquids are incompressible.
How does motion differ between solids, liquids, and gases?
- Solids: Vibrate in fixed positions
- Liquids: Pass by each other
- Gases: Move randomly and freely
Why are solids and liquids incompressible while gases are compressible?
- Solids: Molecules are tightly packed with strong forces.
- Liquids: Molecules are close together with strong forces.
- Gases: Molecules are far apart with weak forces, allowing compression.
What is Brownian motion?
The random movement of particles suspended in a fluid due to collisions with fast-moving molecules in the fluid.
What happens to a dust particle in air?
It moves freely and randomly in a zigzag path and is seen as a speck of light.
Why does Brownian motion occur?
Fast-moving air molecules hit the dust particle from all directions, causing random motion.
How does expansion compare in solids, liquids, and gases?
Expansion in solids < Expansion in liquids < Expansion in gases.
Why do gases expand more than solids?
Gas molecules are far apart with weak forces, allowing more expansion when heated.
What happens to a bimetallic strip when heated?
It bends towards the metal with lower expansion.
Give two disadvantages of expansion.
- Expansion in train railways
- Expansion in electric cables
What is Boyle’s Law?
At constant temperature, pressure is inversely proportional to volume
P₁V₁ = P₂V₂
What happens to gas pressure when volume decreases?
Pressure increases because molecules collide more frequently with container walls exerting more force and pressure.
What is the relationship between pressure and temperature at constant volume?
Pressure is directly proportional to temperature.
What happens to gas molecules when temperature increases?
They gain kinetic energy, move faster, and collide more frequently, exerting more force and pressure.
What is the relationship between volume and temperature at constant pressure?
Volume is directly proportional to temperature.
How do air molecules exert pressure on container walls?
Randomly and freely moving air molecules collide with the walls of the cylinder and rebound causing a change in momentum, which exerts force and pressure
What is the formula for heat energy?
Q = mcΔT
where:
* Q = Energy (Joules)
* m = Mass (kg or g)
* c = Specific heat capacity (J/kg°C | J/g°C)
* ΔT = Temperature change (°C)
What is thermal capacity?
The amount of energy needed to raise the temperature of a body by 1°C.
What is specific heat capacity?
The amount of energy required to raise the temperature of 1 kg/g of a substance by 1°C.
Why do materials with high thermal capacity take longer to heat or cool?
They require more energy to change temperature.
What happens to kinetic and potential energy during a temperature change?
- Kinetic energy increases
- Potential energy remains constant
What happens to kinetic and potential energy during a change in state?
- Kinetic energy remains constant
- Potential energy increases (for melting/boiling) or decreases (for condensation/freezing)
Why does evaporation cause cooling?
The most energetic surface molecules absorb energy from remaining liquid, leaving the remaining liquid with less energy and temperature
How can you increase the rate of evaporation?
- Increase temperature
- Increase air flow
- Increase surface area
- Decrease humidity
- Decrease liquid depth
How does conduction transfer heat (in metals)?
Thermal energy is transferred through metals by conduction. This is due to collisions between vibrating atoms and free electrons through atoms going from the hot to cold part
What materials are good conductors?
Metals (e.g., copper, aluminum) because they have many free electrons.
How can conduction be reduced?
Using insulators like plastic, wood, and rubber.
Where does convection occur?
In liquids and gases.
Why does hot air rise?
It has lower density and is replaced by cooler, denser air.
What is a sea breeze?
Cool air from the sea replaces warm air rising from land.
What is a land breeze?
Cool air from land replaces warm air rising from the sea.
How can heat loss by convection be reduced?
- Using a vacuum
- Using insulators
- Trapping air between layers
- Using a lid
How does radiation transfer heat?
Through electromagnetic (infrared) waves, even in a vacuum.
What are good absorbers of radiation?
Dark, dull, rough, black surfaces.
What are good reflectors of radiation?
Shiny, polished, white, and silver surfaces.
What is the greenhouse effect?
Greenhouse gases trap infrared radiation, increasing Earth’s temperature.
How can Earth’s temperature remain stable?
Incoming radiation from space = Outgoing radiation from Earth.
How does a car radiator lose heat?
- Heat transfers from engine to fluid by conduction.
- Heat transfers from fluid to radiator by conduction.
- The radiator is black with a large surface area to increase radiation emission.
How does a vacuum flask prevent heat loss?
- Double walls with vacuum: Reduces conduction & convection.
- Silvered walls: Reduces radiation loss.
- Lid: Reduces heat loss by convection.
What is the difference between specific heat capacity and thermal capacity?
- Specific heat capacity is the energy required to raise the temperature of 1 kg (or 1 g) of a substance by 1°C,
- Thermal capacity is the total energy needed to raise the temperature of an object by 1°C (specific heat capacity multiplied by its mass).
What are the three primary modes of heat transfer, and what is a key characteristic of each?
- Conduction: Energy transfer via direct collisions between particles (depends on thermal conductivity).
- Convection: Energy transfer through the bulk movement of fluids (driven by density differences).
- Radiation: Energy transfer via electromagnetic waves (does not require a medium).
How do pressure, volume, and temperature relate in an ideal gas (for constant T, V, or P)?
- At constant temperature (Boyle’s Law): 𝑃 ∝ 1/𝑉
- At constant volume: 𝑃 ∝ 𝑇
- At constant pressure: 𝑉 ∝ 𝑇
Why does the temperature remain constant during a phase change even though energy is transferred?
During a phase change, the energy is used to break or form intermolecular bonds rather than increasing the kinetic energy of the particles, so the temperature remains constant until the phase change is complete.
