particle model of matter (p3)

Question 1

describe the arrangements of solids:

Answer 1

• strong forces of attraction between particles, holding them closed together in a fixed position, forming a regular lattice structure
• holds a definite shape and volume, so can’t flow
• particles vibrate

Question 2

describe the arrangement of liquids:

Answer 2

solid particles gain more and more kinetic energy as they heat up, and eventually break free of their bonds, forming a liquid

• weak forces of attraction between particles
• particles are free to move around, random arrangement
• however, particles do tend to stick together and are fairly compact
• definite volume, but shape can change (flow)

Question 3

describe the arrangement of gases:

Answer 3

heating up the liquid even more means the particles move around even faster, gain even more energy and weaken the forces of attraction. at a certain point, these bonds are broken altogether, and the liquid boils/evaporates

• very weak force of attraction between particles, free to move
• no definite shape/volume
• constantly moving with a random motion (straight lines in any direction)

Question 4

what are the two things that can happen when heating a gas?

Answer 4

• particles get more energy
• gas will either expand if the container allows it
• if the container is fixed, so is the volume, and the pressure will simply increase

Question 5

what happens if you cool gases or liquids?

Answer 5

gas particles won’t have enough energy to overcome forces of attraction between particles, so bonds will start to form, forming it into a liquid
- same happens from liquid to solid

Question 6

what happens when substances change state in a closed system?

Answer 6

• won’t change the mass as it’s still the same number of particles
• will change density. solids have the highest, gases have the lowest

Question 7

what is particle theory/kinetic theory?

Answer 7

helps us explain how particles in each state behave by considering each particle as a small, solid, inelastic sphere

Question 8

describe the density of a material:

Answer 8

• the mass for the given volume
  e.g. bricks are high density as they have a high mass packed into their volume

Question 9

how do you calculate the density of a material?

Answer 9

density = mass / volume

density = kilograms per metre cubed

mass = kilograms (kg)

volume = m^3

Question 10

how do you convert between g/cm^3 and kg/m^3?

Answer 10

1 g/cm^3 = 1000 kg/m^3
- multiply the g/cm^3 measurement by 1000

Question 11

when will you get a more accurate density reading?

Answer 11

the larger the mass, the more accurate the density, as it minimises the effects of uncertainty
- you can also take multiple measurements to identify anomalies, or calculate a mean

Question 12

what happens to an object’s mass when it changes state?

Answer 12

nothing happens to the object’s mass - mass is conserved.

Question 13

what stores of energy do particles have in a material?

Answer 13

• potential energy (intermolecular forces and chemical bonds)
• kinetic energy

Question 14

what is internal energy?

Answer 14

the energy stored inside a system by particles (e.g. atoms, molecules) that make up the system.

Question 15

how do you calculate internal energy?

Answer 15

potential energy + kinetic energy of all the particles in the system.

Question 16

what else is increased when we heat a material (e.g. heat a solid to a liquid by melting it)?

Answer 16

we increase the internal energy, as the kinetic energy increases (the particles move more energetically until they have enough energy to escape from their intermolecular bonds). liquid particles have more kinetic energy than solid particles, therefore kinetic energy increases.

• this ends up either heating the object, or if heated enough, can change its state.

Question 17

what is the process called when a solid turns directly into a gas?

Answer 17

sublimation

Question 18

are changes of state physical or chemical?

Answer 18

they’re physical, as if we reverse the change, the material recovers its original properties

Question 19

describe evaporation:

Answer 19

when a liquid turns into a gas, but only on the surface of the liquid. only the particles on the surface have enough energy to evaporate.

Question 20

what is the definition of specific heat capacity?

Answer 20

the amount of energy required to raise the temperature of 1kg of a substance by 1 degree celsius.

• if the temperature of the system increases, the increase in temperature depends on the mass of the substance heated, the type of material, and the energy input to the system .

Question 21

RECAP: what is the equation for specific heat capacity?

Answer 21

change in thermal energy = mass x specific heat capacity x temperature change

Question 22

what is the latent heat of a substance?

Answer 22

the amount of energy required to change the state of 1 kilogram (kg) of a material without changing its temperature.

Question 23

what does a substance’s latent heat depend on?

Answer 23

• type of substance
• amount of substance

Question 24

what is the equation for specific latent heat?

Answer 24

energy for a change of state = mass x specific latent heat.

energy = joules (J)
mass = kilograms (kg)
specific latent heat = joules per kilogram (J/kg)

Question 25

what is the specific latent heat of fusion?

Answer 25

the energy required to change 1kg of a substance from a solid to a liquid with no temperature change

Question 26

what is the specific latent heat of vaporisation?

Answer 26

the amount of energy required to change 1kg of a substance from a liquid to a vapour with no temperature change

Question 27

what is the specific latent heat for cooling?

Answer 27

the amount of energy released by a change in state

Question 28

describe gas pressure:

Answer 28

gas pressure is due to the particles of a gas colliding with the walls of its container, which exerts a pressure. by increasing the number of collisions each second or increasing the energy of each collision, we can increase the pressure (increase the temp. of the gas) - pressure is measured in pascals (Pa)

Question 29

what happens to gas pressure if we increase the temperature?

Answer 29

increasing the temperature transfers energy to the particles' kinetic energy stores, so they move around faster. this leads to more collisions with the container walls, and each collision will involve more force - pressure increases with temperature

Question 30

what happens to gas pressure if we increase the concentration?

Answer 30

increasing the number of particles in the container, but keeping the volume the same, means there'll be more particles to collide with the container walls, meaning more collisions - higher concentration = higher pressure

Question 31

what happens to gas pressure if decrease the volume?

Answer 31

a smaller container with the same number of particles means there'll be more particles per unit of volume. these particles no longer have as far to travel between each collision, therefore there'll be more - as volume decreases, pressure increases, as long as the temperature remains constant

Question 32

what happens if we change the temperature or concentration in an expandable container?

Answer 32

- simply change the volume of the container, rather than the pressure - any increase in the number/force of collisions will cause the balloon to expand, rather than increasing the pressure - however in reality it would probably increase both the volume and pressure

Question 33

define pressure:

Answer 33

the force being exerted per unit of area - pressure = force / area

Question 34

how do particles collide with the container walls?

Answer 34

they collide at right angles to the walls, causing the gas pressure. by increasing the size of the container, we can reduce the gas pressure, as particles must now travel further to collide with the walls.

Question 35

name the equation linking pressure, volume and constant:

Answer 35

pressure x volume = constant pressure = pascals (Pa) volume = metres cubed (m^3) - this is because pressure and volume are inversely proportional, so as one increases, the other decreases, therefore always resulting in a constant value

Question 36

how does an object stay afloat on fluid?

Answer 36

- if the object's density is lower than the density of the fluid, the object will float - the object is kept afloat by a force called 'upthrust'

Question 37

what is the law of displacement?

Answer 37

an object completely submerged in fluid (e.g. water) will replace an amount of fluid equal to its own volume

Question 38

what is work done?

Answer 38

work is the transfer of energy by a force. - doing work on a gas increases the internal energy of the gas and can cause an increase in the temperature of the gas.

Question 39

explain how, in a given situation, e.g. a bicycle pump, doing work on an enclosed gas leads to an increase in the pressure of the gas:

Answer 39

- work is the transfer of energy by a force. - doing work on an enclosed gas (e.g. by using a foot pump on a tyre will lead to an increase in the thermal energy store of the gas, and so the temperature of the gas). - this will lead to an increase in internal energy in the gas. - the average kinetic energy of the particles will be higher, so higher pressure.

Question 40

what is temperature?

Answer 40

the average internal energy of all the particles in a substance - heating objects increases the internal energy of their particles (as it increases their kinetic energy), therefore their temperature increases too

Question 41

why is the graph for the temperature of a substance over time as we heat it not a straight line?

Answer 41

- when the substance reaches its melting or boiling point (changing state), the line plateaus and the object doesn't increase in temperature - this is because the energy provided is being used to weaken or break the forces holding particles together, rather than increasing the particles' internal energy - this is similar on a cooling graph, where instead the energy is being used to form new bonds, which releases energy, counteracting the cooling, which is what keeps the temperature constant during the change in state