P3

Question 1

Define density

Answer 1

The density of a material tells us the mass for a given volume.

Question 2

How to calculate density?

Answer 2

Density = mass / volume

ρ (kb/m3) = m (kg) /V (m3)

Question 3

2 things the particle model can be used to explain

Answer 3

The different states of matter, differences in density

Question 4

Particle arrangement in a solid

Answer 4

Particles are very close together - strong forces of attraction, arranged in a regular pattern, vibrate about their fixed positions

Question 5

Particle arrangement in a liquid

Answer 5

Particles are close together - weaker forces of attraction, not arranged in a regular pattern, can move around each other

Question 6

Particle arrangement in a gas

Answer 6

Particles are very far apart - almost no forces of attraction, not arranged in a regular pattern, moving very rapidly

Question 7

Density of a solid

Answer 7

High density - particles are packed closely together so have a lot of mass for their volume

Question 8

Density of a liquid

Answer 8

High density - particles are close together so have a lot of mass for their volume

Question 9

Density of a gas

Answer 9

Low density - particles are very far apart so only have a small mass for their volume

Question 10

Define regular object

Answer 10

Regular objects have dimensions which are easy to measure, e.g. with a ruler

Question 11

Define irregular object

Answer 11

Irregular objects have dimensions which cannot be easily measured

Question 12

3 steps to determine the density of a regular object

Answer 12

1. Determine the mass using a balance.
2. Work out the volume by using a ruler to measure the length of each side.
3. Calculate the density by dividing the mass by the volume.

Question 13

5 steps to determine the density of an irregular object

Answer 13

1. Determine the mass using a balance.
2. Fill a Eureka can with water (it has a spout so the water can flow out the can).
3. Place the object into the water - will cause the water to be displaced and flow out the can through the spout.
4. Measure the volume of the water displaced using a measuring cylinder.
5. Calculate the density by dividing the mass by the volume.

Question 14

4 steps to determine the density of a liquid

Answer 14

1. Place a measuring cylinder on a balance and press zero.
2. Pour 50ml of the liquid into the measuring cylinder. This is 50cm3.
3. Determine the mass.
4. Calculate the density by dividing the mass by the volume.

Question 15

5 changes of state

Answer 15

Melting, boiling/evaporating, condensation, freezing, sublimation

Question 16

How does melting happen?

Answer 16

Heating a solid transfers energy to the kinetic energy stores of the particles, increasing the internal energy. When the particles have enough energy in their kinetic energy stores, they can break the bonds holding them together and it turns into a liquid.

Question 17

How does boiling happen?

Answer 17

Heating a liquid transfers energy to the kinetic energy stores of the particles, increasing the internal energy. When the particles have enough energy in their kinetic energy stores, they can break the bonds holding them together and it turns into a gas.

Question 18

How does condensation happen?

Answer 18

Cooling the gas reduces the internal energy, forms bonds and it turns into a liquid.

Question 19

How does freezing happen?

Answer 19

Cooling the liquid reduces the internal energy, forms bonds and it turns into a solid.

Question 20

Change of state when sublimation occurs

Answer 20

Solid turning directly into a gas

Question 21

When does evaporating occur?

Answer 21

Evaporation is when only the surface of a liquid turns to a gas. Only the particles on the surface have enough energy to turn into a gas.

Question 22

What type of changes are changes of state and is mass conserved during changes of state?

Answer 22

Changes of state are physical changes which differ from chemical changes because the material recovers its original properties if the change is reversed.
Mass is always conserved.

Question 23

Define internal energy

Answer 23

Internal energy is the energy stored in a system by the particles (atoms and molecules) that make up the system.
It is the total kinetic energy and potential energy of all the particles.

Question 24

Why is there kinetic and potential energy in particles?

Answer 24

The kinetic energy of the particles is due to their movement and the potential energy is due to the forces between the particles and bonds between atoms in a molecule.

Question 25

How does heating change the energy stored within the system?

Answer 25

Heating changes the energy stored within the system by increasing the energy of the particles that make up the system. This either raises the temperature of the system or produces a change of state.

Question 26

What does the increase in temperature of a system depend on?

Answer 26

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

Question 27

Define specific heat capacity of a substance

Answer 27

The specific heat capacity of a substance is the amount of energy required to raise the temperature of 1 kg of the substance by 1°C.

Question 28

What energy is needed for a substance to change state?

Answer 28

The energy needed for a substance to change state is called latent heat.

Question 29

What happens when a change of state occurs?

Answer 29

When a change of state occurs, the energy supplied changes the energy stored (internal energy) but not the temperature.

Question 30

Define specific latent heat of a substance and is it different for different substance / states

Answer 30

The specific latent heat of a substance is the amount of energy required to change the state of 1kg of the substance with no change in temperature. It is different for different materials and for changing between different states.

Question 31

Define specific latent heat of fusion

Answer 31

The energy required to change 1kg of a substance from a solid to a liquid with no change in temperature.

Question 32

Define specific latent heat of vaporisation

Answer 32

The energy required to change 1kg of a substance from a liquid to a vapour with no change in temperature.

Question 33

What happens at the first line of the heating graph?

Answer 33

The temperature of the solid is rising as the energy of the particles increases.

Question 34

What happens at the second line of the heating graph?

Answer 34

The temperature stops rising and the line becomes horizontal. The solid is changing state and turning into a liquid - melting. This is the melting point.

Question 35

What happens at the third line of the heating graph?

Answer 35

Once all of the solid has melted, the temperature of the liquid increases as the energy of the particles increases.

Question 36

What happens at the fourth line of the heating graph?

Answer 36

The temperature stops rising and the line becomes horizontal. The liquid is changing state and turning into a gas - boiling. This is the boiling point.

Question 37

What happens at the fifth line of the heating graph?

Answer 37

Once all of the liquid has boiled, the temperature of the gas increases as the energy of the particles increases.

Question 38

What does changing the temperature of a gas, held at a constant volume, result in?

Answer 38

Changing the temperature of a gas, held at a constant volume, changes the pressure exerted by the gas.

Question 39

Why is there pressure in a gas?

Answer 39

The pressure of the gas is due to the particles colliding with the walls of the container that the gas is held in. By doing this, the gas particles are exerting a pressure.

Question 40

How can there be an increase in pressure of a gas?

Answer 40

The pressure can be increased if the number of collisions per second or the energy of each collision increases.

Question 41

How does increasing the temperature of gas, increase the pressure?

Answer 41

High temperature allows the particles to have a higher kinetic energy - more collisions per second and higher energy collisions. This results in an increase in the total force exerted.