Simple Kinetic Molecular Model of Matter

Simple Kinetic Molecular Model of Matter
● Solids
Molecular model
● Gases
● Liquids
Molecules are compacted
Strong intermolecular forces of attraction
static and cannot be compressed
Molecules close to each other, but in random arrangements
Weak-ish intermolecular forces of attraction
takes the shape of given space, cannot be compressed
Molecules furthest apart in random arrangements and movements
very weak intermolecular forces
completely fills given space and can becompressed
Molecules can only vibrate
Temperature, pressure and volume
Brownian motion
Evaporation
gas molecules move quickly in many directions via collisions with other gas molecules
as temperature increases, average kinetic energy and speed of molecules does too
molecules bounce off wall and change directions, velocity and momentum changes
if temp. increases, pressure increases so molecules collide faster with walls.
if vol. increases, pressure decreases since molecules collide less with the walls.
liquid surfaces slowly turn to gas due to higher energy within molecules
remaining molecules have lower average kinetic energy aka lower temperature.
to increase the rate of evaporation, one must...
Increase temperature
Increase surface area
Draught
Evaporation cools body that touches evaporating liquid (i.e. sweaty skin because liquid absorbs energy from body so that it can evaporate.
Thermal properties and temperature
Thermal expansion
When solid is heated, molecules vibrate more but stay in place, so expansion span is relatively small.
When liquid is heated, it expands like a solid, but intermolecular forces are weaker so it expands more.
When gas is heated, molecules move further apart quickly, so expansion span is the widest among all states.
Melting and boiling
specific heat capacity: amount of energy required to raise temperature of 1kg of substance by 1°C. (∆𝐸=𝑚𝑐∆𝑇)
thermal capacity: how much energy needs to be put in to raise temperature by given amount. (𝒕𝒉𝒆𝒓𝒎𝒂𝒍 𝒄𝒂𝒑𝒂𝒄𝒊𝒕𝒚 = 𝒎𝒄)
... occurs when energy is put in to a body without a change in temperature.
melting point: temperature at which solid will melt when heated.
boiling point: temperature at which liquid will turn into a gas when heated.
condensation: gas molecules come together from lack of energy to become liquid.
freezing: liquid molecules slow down and bond to become more compacted and solid.
evaporation: different to boiling because it occurs at any temperature on liquid surface
specific latent heat
amount of energy needed to change the state of 1kg of a substance.
SLH of fusion = energy to melt/freeze
SLH of vaporization = energy to boil/condense
energy = mass × specific latent heat
When body changes state, energy goes to making molecules more free from each other rather than increasing kinetic energy.
Measuring Temperature
Thermal processes
Conduction
Convection
Radiation
thermal energy in solids/liquids can be transferred via conduction.
non-metals = poor conductors/insulators. ; metals = good conductors.
thermal energy in fluids can be transferred via convection.
... when molecules in fluid with high thermal energy move to area with low thermal energy.
e.g. water boilers and hot air balloons.
thermal energy transferred via infrared radiation (part of the electromagnetic spectrum); doesn’t require medium.
black object with dull texture = best absorbers and emitters of radiation.
white bodies with shiny texture = best radiation reflectors
temperature and surface area increases = more infrared radiation emitted.
Thermocouple
has two different metals that meet
temperature difference between them causes small voltage which causes current flow
if temperature increases, so does current.
used for constantly varying high temperatures
Sensitivity, range and linearity
Liquid-in-glass thermometer
the liquid expands/contracts as temperature rises/falls.
expansion amount can be matched to temperature range.
Sensitivity = change in length/change in temperature (use bigger bulb/narrower bore to increase sensitivity)
Range = difference between maximum and minimum temperatures (use wider bore/longer stem to increase range)
Linearity = change in temperature causes same change in length. (kyk ratio gitu)
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