particle model of matter (p3)

Question 1

describe the arrangements of solids, liquids and gases:

Answer 1

solid: vibrate around a fixed point, regular pattern, very close together, high density (apart from polystyrene)
liquid: close together, no regular pattern, move around each other, high density
gas: particles far apart, no pattern, moving rapidly, low density

Question 2

describe the density of a material:

Answer 2

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

Question 3

how do you calculate the density of a material?

Answer 3

density = mass / volume

density = kilograms per metre cubed

mass = kilograms (kg)

volume = m^3

Question 4

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

Answer 4

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

Question 5

what stores of energy do particles have in a material?

Answer 5

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

Question 6

what is internal energy?

Answer 6

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

Question 7

how do you calculate internal energy?

Answer 7

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

Question 8

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

Answer 8

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 9

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

Answer 9

sublimation

Question 10

are changes of state physical or chemical?

Answer 10

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

Question 11

describe evaporation:

Answer 11

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 12

what is the definition of specific heat capacity?

Answer 12

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 13

RECAP: what is the equation for specific heat capacity?

Answer 13

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

Question 14

what is the latent heat of a substance?

Answer 14

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

Question 15

what is the equation for specific latent heat?

Answer 15

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 16

what is the specific latent heat of fusion?

Answer 16

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

Question 17

what is the specific latent heat of vaporisation?

Answer 17

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

Question 18

describe gas pressure:

Answer 18

• the molecules of a gas are in constant random motion. the temperature of the gas is related to the average kinetic energy of the molecules.
• changing the temperature of the gas, held at constant volume, changes the pressure exerted by the gas.

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 19

how do particles collide with the container walls?

Answer 19

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 20

what is the correlation between the gas pressure and the volume?

Answer 20

they’re inversely proportional. if the volume increases, the gas pressure decreases, as they’re both constants - as long as the container is at a constant temperature.

Question 21

name the equation linking pressure, volume and constant:

Answer 21

pressure x volume = constant

pressure = pascals (Pa)
volume = metres cubed (m^3)

Question 22

how does an object stay afloat on fluid?

Answer 22

• 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 23

what is the law of displacement?

Answer 23

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

Question 24

what is work done?

Answer 24

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 25

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 25

• 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.