the particle model - topic 13 Flashcards
what is density
a substances mass per unit volume
density =
mass/volume
how to measure density of a liquid
- put measuring cylinder on balance and zero the
balance - add 10ml of liquid and record mass
- add 10ml and record mass and volume
- repeat and find average then use density = mass/vol
how to measure density of a solid
- measure object’s mass with balance
- fill eureka can with water and let it drain
- place empty measuring cylinder under spout
- put solid in can and measure vol of water displaced
- density = mass/vol
why are solids solid
strong forces of attraction hold the particles close together in a fixed, regular lattice and there is not much energy in KE stores so they vibrate about fixed positions
why are liquids like they are
they have weaker forces of attraction between particles and some are able to move past each other. They also have more energy in KE stores so they move more randomly
why are gases like they are
they have no forces of attraction and have more energy in KE stores and so are free to move in random directions
kinetic theory of matter
a theory explaining how particles in matter behave by modelling these as tiny balls
internal energy
the total energy that a systems particles have in their KE and potential energy stores
why do particles in a system vibrate and move around
they have energy in their KE stores
more energy in KE store =
faster movement
further apart particles =
more energy in this store
more energy in thermal store =
higher temperature
what does temperature measure
how much energy is in thermal store
when temp increases …..
the particles vibrate and move around faster but the positions of the particles relative to each other don’t change
cooling a system does what to energy
reduces energy of the particles
what is the coldest anything can ever get
-273 degrees celsius
what is absolute zero
as little energy in their KE stores as possible
how to convert temp in C to temp in K
temp in C + 273
how to convert temp in K to temp in C
temp in K - 273
how to go from solid to liquid
melting
how to go from liquid to solid
freezing
how to go from solid to gas
sublimating
how to go from liquid to gas
boiling
how to go from gas to liquid
condensing
what happens to particles and forces when a system is heated and changes state
energy is transferred to potential energy store, particles move apart and forces get weaker
why is mass conserved during changes of state
because the number of particles remains the same, only the properties are changing
what is specific heat capacity
the amount of energy needed to raise the temperature of 1kg of a substance by 1 degrees celsius
change in thermal energy =
mass x specific heat capacity x temperature change
investigating specific heat capacity
- place container on balance and fill with water and record mass
- connect power supply to immersion heater and ammeter which is also connected to heater and put thermometer in water
- measure initial temp and set pd of power supply
- start the stop watch
- current should not change as temp increases
- once temp increases by 10C, stop stopwatch and heater
- Use E=i x v x t to work out energy supplied by heater
- SHC equation and calculate the specific heat capacity
what is specific latent heat
the amount of energy needed to change 1kg of a substance from one state to another without changing its temperature
specific latent heat of fusion
changing state between solid and liquid
specific latent heat of vaporisation
changing state between a liquid and a gas
thermal energy for change of state =
mass x specific latent heat
how do we investigate changing matters of state
- fill beaker with crushed ice + place thermometer in
- set up equipment ( beaker with thermometer on bunsen burner)
- measure initial temp
- start stop watch and turn on bunsen burner
- every 20s, record temp and state of ice
- continue until ice melts and water boils
- turn off stop watch and bunsen burner and plot results
as gas particles move at high speeds
they collide into each other and the walls of the container they are in and when they collide with a surface they exert a force on it.
as temp increases
faster movement and therefore more collisions
what happens to gas pressure and force as temp increases
increase in net force and gas pressure
what happens to the pressure if temp is constant and there is increasing volume
particles get more spread out and hit walls of container less and lowers gas pressure
how are pressure and volume related
they are inversely proportional
what happens to the volume of gas if internal and external pressure is equal
the volume of the gas and container is constant
how does doing work affect temp
it increases its internal energy which can increase its temp
pressure 1 X volume 1
pressure 2 X volume 2
how does heating a system change the energy within the system
heating a system transfers energy to its particles, so heating a system always increases its internal energy of the system which also leads to an increase in temperature or change in state
how do you reduce unwanted energy transfer
wrap the container in a thermally insulating material and place it on an insulating surface.
why does thermal insulation reduce unwanted energy transfer
thermal insulators reduce the rate at which energy is transferred by heating, which means less energy is transferred to the thermal energy stores of the surrounding.
what is the effect of changing the temperature of a gas
the hotter it is, the fasters its particles move. Faster particles and more collisions with the walls of the container in a given time both lead to an increase in net force and gas pressure
what is the effect of changing the volume of a gas
if the temperature is kept constant, increasing the volume of a gas means the particles get more spread out so the particles hit the walls of the container less often and gas pressure decreases
how can gases be compressed or expanded by pressure change
if a container can easily change its size, then any change in these pressures will cause the container to compress or expand
why is density of a substance highest when a solid
the particles are packed close together - there is a lot of mass in a given volume and as density = mass x volume the density is high
why are liquids less dense than solids
because they have fewer particles in a given volume
why are gases less dense than liquids and solids
because gases have particles spaced far apart, a substance in gas form is less dense
