3-PARTICLE MODELS OF MATTER

Question 1

what is density, how is calculated

Answer 1

the measure of the compactness of a substance, it is a substance’s mass per unit volume)
it depends on what the object is made of and how its particles are arranged
(relates the mass of a substance to how much space it takes up ; if you compressed a material ,
its particles would move closer and it would be more dense)
density= mass/ volume

Question 2

explain energy and arrangement of particles in a solid

Answer 2

strong forces of attraction holding particles close in a fixed regular arrangement,
dont have much energy so particles vibrate in their fixed positon-
density is highest as particles are closest together

Question 3

explain energy and arrangement of particles in liquid

Answer 3

weaker forces of attraction between particles - particles are close but can move past each other are form irregular arrangements, -
more energy that particles in a solid,
move in random directions at low speed -
less dense than solids

Question 4

explain energy and arrangement of particles in a gas

Answer 4

no force of attraction between particles,
particles have more energy than liquids and solids
free to move and travel in random directions at high speeds
gases generally less dense than liquids
they have low densities

Question 5

how to find the density of a solid object (practical)

Answer 5

1- use balance to measure its mass
2-if its a regular solid, measure length width and height with ruler - then calculate volume with relevant formula for that shape

3- for irregular solid- find volume by submerging it in eureka can with water , water displaced by object will be transferred to measuring cylinder
4-record volume of water in measuring cylinder - this is the volume of the object
5- mass divided by volume to get density

Question 6

how to find the density of a liquid(practical)

Answer 6

1- place measuring cylinder on a balance and zero the balance
2- pour 10 ml of lquid into measuring cylinder , record the liquids mass
3- pour another 10 ml into measuring cylinder , repeat until cylinder is full, record total volume and mass each time
4- for each measurement, use mass/ volume to find density, 1ml=1cm cubed
5- take average of calculated densities - gives value for density of the liquid

Question 7

what is internal energy

Answer 7

particles move- energy is stored in kinetic energy store
positions of particles transfer energy to potential energy store

internal energy of a system is total energy of its particles in kinetic and potential

Question 8

when does somethings internal energy increase and how does this happen

Answer 8

heating the system transfers energy to its particles (gain energy in kinetic store and move faster) increasing internal energy

leads to a change in temp or change in state
if temp changes, size of change depends on mass of substance, what its made of (specific heat capacity) and energy input.

Question 9

when does a change in state occur

Answer 9

if the substance is heated enough , particles will have enough energy in kinetic energy stores to break bonds that are holding them together

Question 10

what are all the types of changes of state

Answer 10

solid to liquid = melting
liqiuid to solid= freezing
solid to gas=sublimating
liquid to gas= boiling/evaporating
gas to liquid=condensing

Question 11

how is a change of state a physical change

Answer 11

you dont end up with a new substance, it is the same substance you began with but just in a different form, if you reverse a change of state , the substance will reutrn to its origina form and get back its original propeties, number of particles dont change but arrangement changes, mass is conserved

Question 12

explainn what happens to bonds when something is melting or boiling

Answer 12

youre putting in energy so the internal energy increases
energy is used for breaking intermolecular bonds than raising the temp
(flat spots on the graph show energy being transferred not to change the temp)

Question 13

explain what happens to bonds when condensing or freezing

Answer 13

bonds are forming between particles,releasing energy
this makes internal energy decrease
temperature does not go down until all substance has become liquid(condensing) or solid(freezing)
flat parts of the graph show energy transfer

Question 14

what is latent heat

Answer 14

energy need to change the state of a substance

Question 15

what is specific latent heat of a substance

Answer 15

amount of energy needed to change 1kg of it from one state to another without changing its temperature
specific latent heat is different for different materials for changing between different states.
e.g. for cooling, specific latent heat is released by a change in state

Question 16

what is specific latent heat of fusion

Answer 16

the specific latent heat for changing between a solid and a liquid (melting or freezing)

Question 17

what is specific latent heat of vapourisation

Answer 17

for changing between a liquid and a gas (evaporating,boiling and condensing)

Question 18

how do you calculate specific latent heat

Answer 18

energy = mass x specific latent heat

specific latent heat is J/kg

Question 19

what happens when you increase the temperature of a gas

Answer 19

particles in gas are always moving at in random directions and speeds(temp of gas is related to average energy in kinetic energy store of particle)

increase in temp= you transfer energy to kinetic energy stores of its particles
the higher the temp = the higher the average energy= average speed of particles increase

kinetic energy= 0.5 x mass x speed ^2

Question 20

how do colliding gas particles create pressure

Answer 20

gas particles move at high speeds, when they collide, they bang into each other, they exert a force onto what they have collided with,
(in a sealed container, outward gas pressure is total force exerted by all particles in gas on a unit of area of container walls)

faster particles= more collisions= increase in net force = increase in gas pressure

increase in temp= increase in speed and pressure

(BUT if temp is constant, increasing volume of gas mans particles get more spread out and hit walls less - gass pressure decreases )

Question 21

explain relationship between pressure and volume

Answer 21

pressure and volume and inversely proportional, if volume increases, pressure decreases

pressure x volume= constant

Question 22

how does a change in pressure cause a change in volume

Answer 22

the pressure of a gas causes a net outwards force at right angles to the surface of its container.
there is also a force on the outside of container due to pressure of gas around it.
if a container can easily change its size, then any change in these pressures will cause the container to compress or expand, due to overall force’
(eg if a helium balloon is released, it rises, atmospheric pressure decreases with height, pressure outside balloon decreases - causing balloon to expand until pressure inside drops to the same atmospheric pressure)

Question 23

how does doing work on a gas increase its temperature

Answer 23

if you transfer energy by applying a force, you do work, doing work on a gas increases its internal energy, increasing temp
you can do work on a gas mechanically- (bike pump)gas applies pressure to plunger of pump- exerting force
work is done against this force to push down plunger
transfers energy to kinetic energy stores of gas particles-increasing temp, if pump is connected to tyre- it should feel warmer