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describe how particles in a solid are arranged (mention forces and energy):
strong forces of attraction hold the particles together in a fixed, regular arrangement
particles don’t have much energy so can only vibrate in fixed positions
density is highest in this state, as particles are close together so have a lot of mass for their volume
describe how particles in a liquid are arranged (mention forces and energy):
weaker forces mean particles are close together, but can move past each other, forming irregular arrangements
in liquid state, particles will have more energy so can move in random directions at low speeds
less dense than solids, but still have a lot of mass for their volume
describe how particles in a gas are arranged (mention forces and energy):
almost no forces of attraction, so they’re free to move
in gaseous state, particles have more energy so can travel in random directions at high speeds
gases have low densities compared to solids and liquids
they have less mass for their volume
what is the formula for density? (include units of measurement)
what is meant by density?
the mass per unit volume of a substance
RP5: describe a method to calculate the density of a regular object:
use a balance to measure the mass
measure the length, width and height of the object
using the formula, calculate the volume, giving your value in cm3
calculate the density using the density equation
RP5: describe a method to calculate the density of a irregular object:
use a balance to measure the mass
fill a displacement can (aka eureka can) with room temperature water and align a measuring cylinder with the spout
make sure the water level lies below the level of the spout, making sure there isn’t a large gap between the two levels
place the irregular shaped object slowly into the can, ensuring not to drop it from a high distance or cause it to splash
collect the displaced water that comes out of the spout into a measuring cylinder
the volume of the water = the volume of the object
calculate the density using the density equation
RP5: describe a method to calculate the density of a liquid:
place a measuring cylinder on a balance and zero the balance
pour 10ml (10cm3) of the liquid into the measuring cylinder and record the liquid’s mass
pour another 10ml of the liquid into the measuring cylinder and record the total volume and mass
repeat this process until measuring cylinder is full
for each measurement use the density equation to find the density
take an average of all the calculated densities to get an accurate value of the density of the liquid
what is meant by the term internal energy?
the total kinetic energy and potential energy of all the particles (atoms and molecules) that make up a system (object)
what happens when we heat a system?
the system transfers energy to its particles which gain kinetic energy + move faster
internal energy increases
this leads to a change in temperature or change in state if the substance is heated enough
explain the process of heating a solid:
the solid gains internal energy
eventually the particles have enough kinetic energy to break the bonds holding them together
the solid then turns into a liquid (melting)
explain the process of heating a liquid:
as the liquid is heated more, it gains more internal energy
the particles now have even more kinetic energy allowing them to break more bonds
the liquid then turns into a gas (boiling/evaporating)
explain the process of cooling a gas:
internal energy reduced
the particles lose energy + form bonds
the gas turns back into a liquid (condensation)
explain the process of cooling a liquid:
internal energy is reduced even more
the particles lose more energy + form more bonds
eventually the liquid turns into a solid (freezing)
what is meant by sublimation?
when a substance is able to change from a solid to gas, or gas to solid without becoming a liquid
what does it mean if mass is conserved when a change of state happens?
there are no particles lost or gained when a substance changes state
they’re just arranged differently
are changes of state physical or chemical? why?
physical
we end up with the same substance, just in a different form
if we reverse the change, the material will still have its original properties
what is the difference between boiling and evaporating?
boiling is quicker as bubbles of gas form throughout the liquid which rise to the surface + escape
evaporating is slower as particles only leave from the surface of the liquid without producing any bubbles
what is the meant by the specific heat capacity of a substance?
the energy required to raise the temperature of 1kg of the substance by 1oC
what is the formula for specific heat capacity? (include units of measurement)
explain what is happening on this heating graph:
when a substance is melting/boiling energy is still being put in, increasing the internal energy
the temperature of the solid/liquid rises as we increase the energy of the particles
the internal energy is used to break/weaken forces of attraction
during the change of state we are increasing internal energy, but NOT temperature
the flat spots on the graph is where there is a change of state, and energy is transferred by heating (temperature stops rising)
explain what is happening on this cooling graph:
when a substance is condensing/freezing, energy is released, decreasing the internal energy
the temperature of the gas/liquid drops as we decrease the energy of the particles
the internal energy is used to strengthen forces of attraction, to form bonds
during the change of state, we are decreasing internal energy, but NOT temperature
the flat spots on the graph are where there is a change of state, + energy released as heat (temperature stops dropping)
what is meant by the specific latent heat of a substance?
the energy required to change the state of 1kg of the substance with no change in temperature
what is the specific latent heat of fusion?
the energy required to change 1kg of a substance from a solid to a liquid with no change in temperature
what is the specific latent heat of vaporisation?
the energy required to change 1kg of a substance from a liquid to vapour with no change in temperature
what is the formula for specific latent heat? (include units of measurement)
explain how the motion of the molecules in a gas is related to both its temperature and its pressure:
at low temperatures, particles have less kinetic energy
this means there are fewer collisions per second
fewer collisions means less pressure and vice versa
how is pressure created in a gas?
collisions between the particles and the wall of the container holding the gas exert a force (a pressure)
this force acts at right angles to the container walls
the outward gas pressure is the total force exerted by all the particles on a unit area of the container walls
what happens if we increase the volume of a container (keeping the temperature constant)?
the pressure reduces
there is now more space between the particles, so they travel much further before colliding
this reduces the number of collisions per second therefore reducing the pressure
what is the relationship of a gas at fixed mass and constant temperature?
pressure and volume are inversely proportional
if one increases, the other decreases
if we double one we must half the other etc
what happens if we change the pressure of a gas (keeping the temperature constant)?
the pressure of a gas causes a net outward force at right angles to the surface of the container
there’s also a force on the outside of the container due to the pressure of gas around it
if the container can easily change size (e.g. balloon) the overall pressure can cause container to contract/expand
what happens if work is done on a gas? give an example:
energy transferred to the gas particles increasing internal energy of the gas
this causes an increased temperature of the gas
e.g. in a bike pump, gas applies pressure to the plunger of the pump, exerting a force
work has to be done against this force to push down the plunger
kinetic energy increases, raising the temperature
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