Thermal Physics Flashcards
Describe particle motion in solids.
vibration about a fixed position
Can solids be compressed?
no
Do solids have a fixed shape?
yes
Do solids have a fixed volume?
yes
How are the forces of attraction/bonds between molecules in a solid?
strong
How are molecules arranged in solids?
regular arrangement, molecules close together, tightly packed
Describe particle motion in liquids.
Particles flow and move over each other
Can liquids be compressed?
no
Do liquids have a fixed shape?
no
Do liquids have a fixed volume?
yes
How are the forces of attraction/bonds between molecules in a liquid?
weaker than in a solid
How are molecules arranged in liquids?
molecules are close together, irregular arrangement
Describe particle motion in gases, and the shape they take.
molecules are free to move, move randomly, all directions
take shape of container
Can gases be compressed?
yes
Do gases have a fixed shape?
no
Do gases have a fixed volume?
no
How are the forces of attraction/bonds between molecules in a gas?
weak forces of attraction, molecules far apart
What is internal energy?
energy of the molecules of a body
What is kinetic energy?
energy due to molecule movement
What is potential energy?
energy due to forces and separation of molecules
The greater the ______ of the molecules, the greater the potential energy
separation
In potential energy, what is the type of force?
electrical
solid -> liquid
melting
gas -> liquid
condensation
liquid -> solid
solidification
for water, freezing
liquid -> gas
boiling or evaporation
In order to weaken/break bonds between molecules, what do melting and boiling do?
absorb heat energy
Which processes absorb heat energy? Why?
melting and boiling
to weaken and break bonds between molecules and increase molecule separation
What happens as temperature increases, to particles?
they move faster
What is the lowest possible temperature (absolute 0)?
-273 celcius degrees
What does it mean to the particles if an object is at absolute 0?
particles have the least kinetic energy
- temperature at which particles in a gas exert no pressure and are no longer moving, hence not colliding with their container
Describe the pressure of a gas, relation to motion of its particles and their collisions with a surface.
moving gas molecules collide with a surface, exerting a force.
What is the effect of temperature on gas pressure? Why?
since molecules will move more quickly, they will collide with the walls of the container/surfaces more often, exerting a greater pressure
positive correlation
What is one piece of evidence for the kinetic particle model of matter?
random movement of particles in suspension
Describe Brownian motion.
Brownian motion is the random collision between particles in suspension and the particles of the gas/liquid
What causes pressure in gases?
force exerted when a particle collides with surfaces (creates F/a)
What is Boyle’s law?
For a fixed mass of gas at constant temperature, pressure is inversely proportional to volume
What happens to the pressure of a gas as volume increases, at constant temperature?
decreases
Why is pressure higher when volumes are smaller?
molecules collide off walls of the container more often.
What is the formula to find out pressure and volume before and after?
P1V1=P2V2
What happens to the pressure of a gas when temperature changes (volume constant)?
pressure increases as temperature increases
Why is pressure higher at higher temperatures?
molecules move faster and collide with container walls more often.
What is the equation relating degrees K and C?
T (in K) = 0 (in C) + 273
Which processes emit heat energy? Why?
solidification and condensation, to strengthen or make molecular bonds and decrease molecule separation
What is temperature, in terms of molecules?
measure of the average kinetic energy of the molecules of a substance
How is the graph for P x V = constant?
For a fixed mass of gas at constant temperature, what is the relationship between pressure and volume?
P x V = constant
What happens when a material receives heat energy, in terms of expansion?
molecules move faster, molecules separate further. the material will expand
What happens when a material loses heat energy, in terms of expansion?
molecules move slower, molecules come close together. the material will contract
Which state of matter expands most, for the same amount of heat energy?
Why?
gases, no forces of attraction between molecules, molecules have enough energy to overcome the weak intermolecular forces
Which state of matter expands the least, for the same amount of heat energy?
Why?
solid, because the molecules cannot overcome the strong intermolecular forces holding the molecules together
If a gas and a solid are subject to the same amount of heat energy, which will expand more?
gas
What are 3 applications of thermal expansion in everyday life?
gaps in railway tracks
fitting metal tyres onto railway train wheels
bimetallic strips
thermometers
Why are there gaps in railway tracks?
because it leaves space for solids to expand into when temperature increases
How is thermal expansion used to fit metal tyres onto railway train wheels?
since the wheel is bigger than the tyre, the tyre is heated so it expands. this will make it possible for it to fit over the wheel. then it is cooled to contract.
How does a bimetallic strip work?
two different materials on either side of a strip. when it is heated, the material which expands more will expand and cause the strip to bend (vice verse for cooling)
What is the relative order of magnitudes of the expansion of solids, liquids and gases?
(least expansion) solid - liquid - gas (most expansion)
What causes an increase in internal energy?
rise in temperature of an object
In terms of molecules, what does an increase in temperature mean?
increased average kinetic energy of molecules of a substance
Define the term ‘specific heat capacity’.
the heat energy needed for a body of mass given to increase its temperature (by 1 degree)
What is the equation for specific heat capacity?
c= ∆E / m∆θ
Describe an experiment to find out the s.h.c of water.
- Connect electrical heating element to power supply
- Connect ammeter through the heating element and a voltmeter to measure the pd across it
- Measure water into polystyrene cup, record temperature
- Turn on heater
- Place heater into cup, allow it to warm the water for 5 minutes while recording the current and pd
- Turn off heater, measure temp of the water
- Calculate the energy provided by heater P = IV and E =Pt
- Calculate s.h.c
How do thermometers use thermal expansion?
mercury expands as the temperature increases
What happens to the temperature of a substance as it goes from a solid to a liquid?
it will increase until the melting point is reached. the temperature stays constant until the substance is a liquid.
What happens to the temperature of a substance as it goes from a liquid to a gas?
it will increase until the boiling point is reached. temperature stays constant until the substance is a gas.
Name 3 differences between boiling and evaporation.
boiling only occurs at boiling point
evaporation is much slower
evaporation is only at the surface, unlike boiling which is throughout
boiling forms bubbles
boiling requires an external thermal energy source
What is condensation, in terms of particles?
when a gas cools down, the particles move more slowly
they do not have the energy they had to overcome the intermolecular forces
particles get closer together and form a liquid
What is solidification, in terms of particles?
when a liquid cools down, the particles move more slowly
they do not have the energy they had to overcome the intermolecular forces
particles get closer together and form a solid
Define ‘evaporation’.
the escape of more energetic particles from the surface of a liquid
Evaporation has a ______ effect.
cooling
How does evaporation cool down a liquid?
molecules with a higher KE escape, leaving behind molecules with less KE. this causes the liquid to cool down.
What is one example of evaporation’s cooling effect in real life?
sweating
How does sweating work?
water evaporates from our skin, the temperature of the water falls, and removes heat energy from our body
What are factors that influence the rate of evaporation?
temperature
wind
surface area
How does temperature influence the rate of evaporation?
molecules move faster, can escape surface of liquid
increased temperature, increased rate of evaporation
How does wind influence the rate of evaporation?
decreases number of molecules above the liquid surface, leaving space for them
increased wind, increased rate of evaporation
How does surface area influence the rate of evaporation?
more molecules are positioned at the surface and can escape
increased surface area, increased rate of evaporation
How is heat transferred in solids (conduction)?
the particles which vibrate about a fixed spot gain energy, colliding with the particles next to them and transferring thermal energy
Define ‘conduction’
Where does it occur?
transfer of thermal energy from one object to another. occurs in solids
Why are metals good thermal and electric conductors?
their delocalised electrons can move throughout the metal
How does conduction occur via delocalised electrons?
electrons gain ke from hot end of metal, moving and colliding with atoms, increasing their KE and temp.
Why are gases poor thermal conductors?
the particles are far apart, making it hard for energy to be transferred from one particle to another
why are liquids and gases poor conductors
particles are too far from each other and rarely make contact to transfer energy
What is one experiment to test conductivity?
put boiling water in a box with holes
place rods of different materials in these holes
place drawing pins held with petroleum jelly on the far ends of rods
see which drawing pins fall of first due to conduction of heat from water
Define ‘convection’
method of thermal energy transfer in liquids and gases
How does convection work in liquids/gases? What is the name given to this movement?
hot fluid expands, becomes less dense and rises
cold fluid sinks as it is more dense
the colder fluid is then heated and rises again, forming a convection current
What is a convection current?
movement of fluid that transfers heat energy upwards
Describe one experiment to test convection
fill a beaker with water, then place a potassium manganate crystal into the beaker
place a bunsen burned flame right under the crystal
you will see the convection from the movement of color in the beaker
Define ‘radiation’
heat transfer from a hot to a colder place by infrared electromagnetic waves
Which object emit thermal/infrared radiation?
all of them :)
Does infrared radiation require a medium?
no, like all electromagnetic waves
Which colours and textures are good emitters and absorbers of heat energy?
dark colours (black)
dull textures
Which colours are poor emitters and absorbers of heat energy?
white/shiny colours
Which colours are good reflectors of heat energy?
white/shiny colours
In terms of energy, what is necessary for an object to be at a constant temperature?
transfer energy away from object at same rate that it receives energy
How does the Earth’s average temperature remain constant?
infrared radiation energy per second absorbed from sun is balanced by i.r energy per second emitted to space
What is one experiment to test good/bad emission of infrared radiation?
place two metal cans (one silver, one matte black) with hot water, a thermometer and a lid on them
observe that the black one cools down faster since they emit better
What is one experiment to test good/bad absorption of infrared radiation?
take two metal cans (one matte black, one silver) with water, a thermometer and a lid on them
place them equidistantly from an electric radiant heater
black will heat up faster since it absorbs heat better
What are two factors affecting rate of emission of radiation?
- surface temperature
- surface area
The hotter an object is, the ____ infrared radiation it emits.
more
A bigger object (larger s.a) emits ____ radiation than a smaller object (ignoring other factors)
more
objects with _____ surface areas will absorb more radiation than those with ______ surface areas.
large
small
applications/consequences of thermal expansion
- metal railway track expand and start to curve (buckling)
- buckling of road surfaces
- buckling of bridges
expansion of solids
- expand slightly
- low energy molecules overcome th strong intermolecular force
expansion in liquids
- expand more than solids
- molecules have enough energy to partially overcome the intermolecular force
expansion in gases
- expand the most
- molecules have high energy to overcome the intermolecular force
what is internal energy
total energy stored in a system by the particles that make up the system due to their motion and positions
what is specific heat capacity
Energy required to change the temperature of 1 kg of the substance by 1 °C.
evaporation
- occurs to any liquid at any temp and results in the cooling of the liquid
- molecules that hit the surface provide energy
melting and boiling point of water
0 and 100
boiling
- occurs to a liquid at certain temp and involves temperature input
- does not result in cooling of the liquid
