Unit 2 - Thermal physics Flashcards
Properties of solids
- High density
- Can’t flow
- Fixed volume
- Fixed shape
- Can’t be compressed
- Regular arrangement
- Particles oscillate in a fixed position
Properties of a liquid
- High density
- Can flow
- Fixed volume
- No fixed shape - takes the shape of a container
- Particles flow over each other
- Can’t be compressed
Properties of a gas
- Low density
- Can flow quickly
- Can be compressed
- No fixed shape - takes the shape of a container
- No fixed volume - takes the volume of a container
- Can be compressed
Solid –> Liquid
Melting
Liquid –> Gas
Boiling
Solid –> Gas
Sublimation
Gas –> Liquid
Condensation
Liquid –> Solid
Freezing/solidifying
Gas –> Solid
Deposition
Melting point
The temperature a solid changes state to a liquid
Boiling point
The temperature a liquid changes to a gas
Molecular structure of solids
- Regular arrangement
- Particles are closely packed together - held by strong attractive forces
- Particles are not free to move
- Particles oscillate in a fixed position
Molecular structure of liquids
- Molecules are close together
- Irregular arrangement
- Particles can move/flow past each other
- Weaker intermolecular forces than solids
Molecular structure of gases
- Particles have more energy than solids and liquids
- Particles are far apart/ not touching
- Irregular arrangement
- Very weak or no intermolecular forces
Particles during cooling
- Particles slow down
- Particles come closer together and move slowly enough for forces to make them change state
- States change except for solid which particles just vibrate less
Absolute Zero
0˚K / -273˚C
Relationship with molecules and temperature
As the particles vibrate more frequently, temperature rises
Brownian motion
The free and random motion of particles
Pressure equation
Pressure = Force ÷ Area
Pressure in a container
Caused by the particles in the container colliding with the walls of the container, exerting a small force due to a change in momentum
Relationship with temperature and pressure
- As temperature increases in a container, pressure increase because particles are moving faster and collide with walls more frequently
Relationship with pressure and volume
- Inversely proportional
- As volume decreases, particles have to travel decrease distance and have more frequently collisions, pressure increases
- As volume increases, particles have to travel increased distance and have less frequent collisions, pressure decreases
- Pressure = constant/volume
Relationship with kelvin and celsius
- 0 Kelvin = -273C
- 1 degree kelvin = 1 degree celsius
Thermal expansion
The increased distance between particles (mostly in solids) due to an increase of temperature causing an increase in particle movement
Quantity of thermal expansion by state
- Solids - expand the least
- Liquids - expand more than solids
- Gases - can expand the most
Internal energy
The sum of potential energy and kinetic energies of the particles inside an object
Relationship with temperature and internal energy
As temperature increases, internal energy increases because kinetic energy of particles increases
Factors on amount of internal energy stores by an object
- Mass - greater the mass, greater the amount of energy stored
- Temperature - greater temperature, more energy stored
- Material - some materials require more energy to increase temperature than others
Specific heat capacity
The amount of energy needed to raise 1kg of a material by 1˚C
Equation of specific heat capacity
Specific heat capacity = Change in energy ÷ (Mass x change in temperature)
Units for Specific heat capacity
J/Kg˚C
Water Specific heat capacity
4200J/Kg˚C
Uses of water due to high specific heat capacity
- Heating and cooling systems
- Central heating
- Car radiators
Difference of boiling and evaporation
- Boiling happens at a specific temperature
- Evaporation happens at a range of temperatures
Evaporation’s cooling effect
Since particles with the most kinetic energy escape, lowering the average kinetic energy of the liquid, lowering the temperature of liquid
Molecules in evaporation
The molecules with the most kinetic energy at the surface break their bonds and escape the liquid,
Factors affecting the rate of evaporation
- Surface area - increases surface area increases rate of evaporation because more particles can escape
- Temperature - increased temperature increases rate of evaporation since more particles have enough kinetic energy to escape
- Wind/air flow - Increased airflow increases rate of evaporation because saturated vapor clears making it easier for particles to escape
Types of energy transfer
- Conduction
- Convection
- Radiation
States of matter that use conduction
Solids
Thermal conductors
Materials that are good are transferring thermal energy via conduction
Thermal insulators
Materials that are bad at transferring thermal energy via conduction
Units for conductivity
W/m^2
Molecules in conduction
Particles vibrate more at higher temperatures, which causes the particles surrounding to vibrate more and eventually a temperature increase via lattice vibration
Reason for metals being good conductors
- Presence of free electrons that can move freely and collide with atoms, causing increased vibrations
Conduction in gases and liquids
- Gases - poor conductors because particles are far apart
- Liquids - poor conductors because particles are further apart than solids and flow
States of matter that use convection
- Fluids (liquids and gases)
Convection Currents
- Fluids heats up and expands making it less dense
- Less dense materials float to the top
- Less dense material will cool at the top, condense, become more dense and sink to the bottom
- Fluid circulates
Sea breezes (Convection currents)
- Day - land warms faster due to lower SHC than sea and rises above, drawing cool air from the water to the land
- Night- Due to higher SHC water cools slower and hence rises, drawing cool air from land to water
Relationship with temperature of objects and infrared radiation
The hotter the object the more infrared radiation emitted
Electromagnetic spectrum
The full range of radiation (e.g. infrared) organized by frequency or wavelength
Radiation in a vacuum
Radiation can travel through a vacuum e.g. Sun to Earth
Three affects of radiation
- Emits more than absorbs - cools
- Absorbs more than emits - warms up
- Emits and absorbs the same - constant temperature
Radiation and surface color
- Silvered surface are poor absorbers - they reflect
- Black surfaces are good absorbers
Radiation and surface texture
- Shiny smooth surfaces - increases reflectiveness/ not good absorber
- Dull colored surfaces - better emitters and absorbers
- Rough surfaces - better emitters and absorbers
Radiation and surface area
The larger the surface area, the more radiation emitted and absorbed
Features of vacuum flasks to reduce thermal energy transfer
- Lid - filled with air and foam (insulators) to reduce conduction
- Small gap - Reduces conduction from outer and inner surfaces
- Vacuum - totally prevents conduction and convection - no particles
- Silver surface reduces emissions and absorption of infrared radiation
- Flask - stops liquid from heating or cooling by preventing energy transfer into or out of center
- Insulated supports - reduces conduction to outer casing
Reducing heat loss in houses
- Walls made of poor conductors
- Thick carpets to reduce conduction through floors
- Double glazed windows to reduce conduction and good insulator
- Lofts insulated to reduce air flow
- Outside painted light colors to reduce emission of radiation
