Chapter 5 Flashcards
Kinetic theory
Matter is made up of tiny particles which are constantly in motion. The particles attract each other strongly when close together, but this attraction weaken when they are further apart.
Particles in a solid (according to kinetic theory)
Fixed shape and volume, vibrate around fixed positions, very close together, very strong attraction
Particles in a liquid (according to kinetic theory)
Has a fixed volume no fixed shape, particles are close and attract eachother, can change positions
Particles in a gas (according to kinetic theory)
Has no fixed shape or volume, particles are far apart and do not attract eachother
Brownian Motion
Random movement of particles due to collisions with other particles
Random movement of particles due to collisions with other particles
Brownian Motion
Internal energy
The total kinetic and potential energies of all the atoms or molecules of a material, sometimes the term is used interchangeably with thermal energy
Liquid-in-glass thermometers
The liquid expands and moves up a tube when temperature rises
Thermistor thermometer (thermistor)
Becomes a better electrical conductor when its temperature rises, causing a (higher) current to flow (which can cause a higher reading on a meter)
Thermocouple thermometer
two different metals are joined to form two junctions, a greater difference in temperature between the two junctions causes a voltage which makes a current flow
What is temperature?
the temperature of a material is the average kinetic energy of all the particles in the material. Individual molecules cannot have temperature.
properties of liquid-in-glass thermometers
- sensitivity, how far the thread moves for a constant temperature change
- range, how high and low the thermometer can show
- responsiveness, how fast it responds to a change in temperature
- linearity, how well the calibration agrees with the true value
How to make a thermometer more sensitive
Thinner tube
How to make a thermometer more responsive
Thinner glass, smaller bulb
Range of alcohol thermometers
-115 to 80 degrees
Range of mercury thermometers
-40 to 500 degrees
What is thermal expansion
The expansion of a material when it is heated due to particles having more energy and therefore vibrating more violently, which takes up more space
What is a bimetal strip
Strips of two different metals merged together. When heated, one type of metal expands more than the other, making the strip bend.
In terms of momentum, why does the pressure of a gas increase with temperature?
- Molecules move faster due to more energy
- So there is an increase in velocity
- So that means there is a greater change in momentum
- Which means there is a larger force
- Which means there is a larger pressure
Conduction
Energy from faster-moving particles is passed on by passing on extra motion to slower particles, and by free electrons (in metals)
How to increase conduction
- increase temperature difference
- increase cross-sectional area of the object
- reduce the length of the object
- change the material of the object
How to increase amount of thermal radiation given out
- higher surface temperature
- higher surface area
Emitters
Surfaces that are best at emitting thermal radiation
Good emitters are also good absorbers
-matt black surfaces are best
-shiny surfaces are worst
Absorbers
Surfaces that are best at absorbing thermal radiation
Good absorbers are also good emitters
-matt black surfaces are best
-shiny surfaces are worst
Reflectors
Surfaces that are best at reflecting thermal radiation
Good reflectors are poor emitters and absorbers
-shiny surfaces are best
-matt black surfaces are worst
Features of a vacuum flask
- a stopper to reduce conduction and convection
- A double-walled container with a vacuum between the two, air has been removed to reduce conduction and convection
- Walls with silvery surfaces to reduce thermal radiation
How to increase evaporation
- Increase the temperature
- Increase the surface area
- Blow air across the surface
thermal capacity =
thermal capacity = mass x specific heat capacity
thermal capacity = energy/temperature change
energy transferred in fusion/vaporization =
energy transferred in fusion/vaporization = mass x specific latent heat
Meaning of specific latent heat
Specific latent heat, measured in J/kg, is the amount of energy needed to change each kilogram of a substance into a different form
Meaning of thermal (heat) capacity
Thermal capacity, measured in J/°C, is the amount of energy that must be supplied to raise the temperature of a material by 1°C
Meaning of specific heat capacity
Specific heat capacity, measured in J/kg°C, is the amount of energy needed to raise the temperature of 1kg of a substance by 1°C
Why do gases expand more than liquids, and liquids expand more than solids when heated?
In a solid, the attractions are very strong so they do not move very far apart. In a liquid they are less strong and in a gas they are almost non-existent so particles can move very far away from eachother.
Explain latent heat
While changing state, the material continues to absorb energy, but it does not change temperature as this energy is being used to separate particles rather than increase the temperature. This energy absorbed is known as latent heat.
