Particle model of matter Flashcards
Solids - arrangement of particles
particles are very close together
- particles are arranged in a regular pattern
- particles vibrate but they do not move from place to place
liquids-describe the arrangement of particles
- particles are close together
- particles are not arranged in a regular pattern
- particles can move around each other
Gas- arrangement of particles
- particles are very far apart
- particles are not arranged in any pattern
- particles are moving very rapidly
what is density
Density of a material tells us the mass for a given volume
what is the density of a brick like
A brick has very high density. it has lots of mass packed into its volume
what is the density of a polystyrene block like
the density for a polystyrene block is low. it has a lower mass packed into its volume
what is the equation for density and the units
density
p kg/m^3 = mass (kg) / volume (m^3)
a block of wood has a mass of 150kg and a volume of 0.3m^3. calculate the density
150/0.3=500kg/m^3
solids usually have a very high density why?
solids have a very high density because the particles are very closely packed together solids have lots of mass for their volume.
liquids also usually have high density why?
liquids usually have high density because the particles are close together, liquids have alot of mass for their volume
gases usually have a low density why?
gases have a low density because the particles are far apart so gases only have a small mass for their volume.
there is an exception: polystyrene is a solid with a low density why?
this is because polystyrene has a very open structure and is full of air spaces. it has a small mass for its volume.
required practical density: calculating the density of regular and irregular objects definition of density: density of a material tells us the mass for a given volume
units for density= kg/m^3
regular objects have dimensions we can easily measure with a ruler
irregular objects- cannot easily measure dimensions
regular objects density- first determine the mass using a balance.
next work out volume by using a ruler to measure length of each side. volume of a cube= length of side^3
why cant we measure density of irregular objects using a ruler
because we cannot easily measure the dimensions instead we have to determine the volume using displacement.
how to determine the density of irregular objects
first, measure mass of object using a balance.
fill a eureka can with water. eureka can has a spout so that water can flow out through the spout.
place the object in water. this will cause water to be displaced as it will flow through the spout
collect water in a beaker and then transfer to measuring cylinder to measure the volume of water displaced.
once you have determined the volume, use it to calculate the density of the object using the equation
density kg/m^3= mass (kg)/volume (m^3)
key point- the volume of water displaced is the volume of the object.
what types of energy do particles have
two types: k, p
-kinetic energy= all these particles have kinetic energy (due to particles movement)
potential energy= ( intermolecular forces or chemical bonds if they are a molecule)
what is the definition of internal energy
internal energy is the total kinetic energy and potential energy of all the particles ( atoms or molecules) that make up a system.
total kinetic energy and potential energy of all the particles that make up a system
what happens when we heat a solid
if we heat a solid, we are increasing the internal energy. at some point the solid can turn into a liquid (melting)
what happens to the internal energy if we heat a solid
it increases
what happens when we heat a liquid
when we heat a liquid, again the internal energy increases, at some point the liquid turns into a gas (boiling)
what happens when we cool down a gas
the internal energy reduces the gas turns into a liquid at some point (condensing)
if we cool down the liquid further, we reduce the internal energy even more eventually the liquid turns into a solid ( freezing)
what does it mean if a solid turns directly into a gas
sublimination
when changes of state takes place - mass is always conserved
we are not adding or taking away particles
are changes of state, physical changes or chemical changes
physical changes if we reverse the change, the material recovers its original properties.
what is evaporation
evaporation is when a liquid turns to a gas but only on the surface of the liquid
only particles on the surface have enough energy to change into a gas
what is the definition of specific heat capacity
the specific heat capacity of a substance is the amount of energy required to raise 1kg of the substance by 1 degree celsius.
calculate the energy required to increase the temperature of 2kg of water from 20 degrees celsius to 100 degrees celsius. the specific heat capacity of water is 4200 j/kg degrees celsius
change in thermal energy= mass x specific heat capacity x change in temperature
2 x 4200 x 80= 672000joules
672 KJ
An iron has a aluminium plate with a mass of 1.5 kg. calculate the thermal energy stored in the plate when the temperature rises from 20 degrees celsius to 200 degrees. specific heat capacity of aluminium is 913/j kg degrees celsius
change in thermal energy= mass x specific heat capacity x change in temperature
246510 joules
A hot water bottle cools down from 80 degrees celsius to 20 degrees celsius releasing 756000 joules of thermal energy. calculate the mass of the water in the hot water bottle. the specific heat capacity of water is 4200 j/kg degrees celsius
756000=mx60x4200
mass = 3kg
heating and cooling graphs
recap point- internal energy is the energy stored inside the system by the particles
- the temperature of the solid rises as we are increasing the energy of the particles at some point the temperature stops rising and the line becomes horizontal at this point solid is changing state and becoming liquid (melting)
what happens when the solid is melting (graph)
horizontal line- solid is melting its turning into liquid, the energy we are putting in is weakening or breaking the forces of attraction between the particles, allowing the substance to turn into liquid
what is the energy we are putting in doing
the temperature of the solid is rising as we increase the energy of the particles. the temperature stops rising, horizontal line, the energy we are putting in is weakening ot breaking the forces of attraction between the particles, allowing the substance to change from solid to liquid
what is the energy needed for a substance to change state called
the latent heat
when the substance is changing state why is this shown by a horizontal line
during the change of state, we are increasing the internal energy store of the system but we are not changing the temperature.
what is the melting point
the temperature the substance melts at
why does the temperature start to rise again
all of the solid has melted into liquid and the temperature starts to rise again because we are increasing the energy of the particles .at some point the temperature stops increasing, and the line becomes horizontal again
what does the line becoming horizontal mean this time ( after melting)
at this point the substance is boiling the energy we are putting in is weakening or breaking the forces of attraction between the particles. once all the liquid has boiled,the temperature starts to rise again because we are increasing the energy of the particles.
Cooling graph
if we take a gas and cool it down we can produce a cooling graph
when we cool the gas down, we are decreasing the internal energy of the particles the gas turns into a liquid at some point ( condensing)
if we further cool down the liquid, we reduce the internal energy even more, and eventually the liquid turns into a solid ( freezing)
why does the temperature decrease on a cooling graph
because we are decreasing the energy of the particles
specific latent heat full definition
specific latent heat of a substance is the amount of energy required to change the state of one kilogram of a substance with no change in temperature
specific latent heat of fusion
the energy required to change one kilogram of a substance from solid to liquid with no change in temperature
specific latent heat of vaporisation
energy required to change 1kg of a substance from a liquid to vapour with no change in temperature
specific latent heat equation
E= M x L
energy required to change state (J)
mass = kg
specific latent heat = j/kg
calculate the energy required to convert 0.5kg of ice to liquid water. the specific latent heat of fusion of the water is 334000 j/kg
E=mx l
0.5x334000= 167000 J
calculate energy required to convert 0.15kg of ethanol from liquid to a vapour. the specific latent heat of vaporisation of ethanol is 846000j/kg
E= mx l
0.15 x 846000= 126900 J
Solids: • have a fixed shape • are difficult to compress (to squash). Gases: • will spread and fill the entire container • are easy to compress (to squash). Use your knowledge of kinetic theory to explain the information given in the box. You should consider: • the spacing between the particles • the movement of individual particles • the forces between the particles.
Solids
• (particles) close together
• (so) no room for particles to move closer (so hard to compress)
• vibrate about fixed point
• strong forces of attraction (at a distance)
• the forces become repulsive if the particles get closer
• particles strongly held together / not free to move around (shape is fixed)
any explanation of a property must match with the given
aspect(s) of the particles.
Gases
• (particles) far apart
• space between particles (so easy to compress)
• move randomly
• negligible / no forces of attraction
• spread out in all directions (to fill the container)
how to find the density of the liquid=
- place a measuring cylinder onto a balance and zero the balance
- pour 10ml of liquid into the measuring cylinder and the measure and record the mass of the liquid
- add another 10ml and repeat the process until the cylinder if full
- take the total volume and total mass each time
- use the formula to calculate the density of each measurement
- take an average of the calculated densities
- this will give the value for the density of the liquid
