Particle Model of Matter

Question 1

What is the equation for density? What are its units?

Answer 1

density = mass / volume
units are: kg/m^3 or g/cm^3

Question 2

What is the arrangement and closeness of particles in a solid, liquid and gas?

Answer 2

Solids:
Regular arrangement
Paricles are very close together

Liquids:
Random arrangement
Particles are close together - mostly touching, and there’s no space for another particle

Gases:
Random arrangement
Particles are far apart (large compared to others), not touching; plenty of space between them

Question 3

What is the motion, forces and properties of particles in a solid, liquid and gas?

Answer 3

Solids:
Motion - vibrating around fixed positions
Forces - strong
Properties - rigid, incompressible, dense

Liquid:
Motion - moving a bit + still touching other particles (but not vibrating)
Forces - less strong/weak
Propertires - not rigid, can flow; incompressible; less dense

Gas:
Motion - random directions at a range of speeds; colliding with each other and container walls (not vibrating)
Forces - none or very weak
Properties - fill their container; compressible; very low density

Question 4

Draw a model of a solid, liquid and a gas.

Question 5

Required practical 5.

Question 6

What is the difference between a chemical change and a physical change?

Answer 6

In a physical change, the material recovers its physical properties if the change is reversed.

Question 7

What are the different changes of state?

Answer 7

Solid to liquid: melting
Liquid to gas: boiling
Gas to liquid: condensing
Liquid to solid: freezing
Solid to gas: subliming
Gas to solid: depostion

Question 8

True or false - boiling 1kg of water produces 1kg of steam.

Answer 8

TRUE! Boiling 1kg of water produces 1kg of steam, a gas. Gases have mass just like liquids and solids - if you boil water and none of it is left in the kettle, the water particles have not been destroyed.

Question 9

Is there a difference between “freezing point” and “melting point”?

Answer 9

No - for example, at 0 degrees, water can exist as either a solid or liquid.

Question 10

Does freezing mean being cold?

Answer 10

FREEZING DOES NOT MEAN COLD - wax freezes at 80 degrees, which we don’t consider cold.

Question 11

What is internal energy?

Answer 11

Energy is stored in a system by the particles (atoms and molecules) that make up the system. This is called internal energy.

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

Question 12

How does heating change the energy stored within the system?

Answer 12

Heating changes the energy stored in a system by increasing the energy of the particles that make up that system. This either raises the temperature of the system (increases kinetic energy - energy of random thermal motion) or produces a change of state (increases potential energy).W

Question 13

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

Answer 13

If the temperature of a system increases, the increase in temperature depends on: the mass of the substance heated
the type of material
the energy input to the system

Question 14

What equation links to temperature changes in a system?

Answer 14

changes in thermal energy = mass * specific heat capacity * temperature change

Question 15

What is the specific heat capacity of a substance?

Answer 15

Specific heat capacity of a substance is the amount of energy required to raise the temperature of 1kg of a substance by 1 degree celsius

Question 16

What is latent heat?

Answer 16

Latent heat is the energy needed for a substance to change state. When a change of state occurs, the energy supplied changes the energy stored (internal energy) but not the temperature.

Question 17

What is the specific latent heat of Fusion?

Answer 17

The Specific Latent Heat of Fusion is the energy required to change 1kg of a substancne from the solid state to the liquid state without changing its temperature.

Question 18

What is the specific latent heat of Vaporisation?

Answer 18

Specific Latent Heat of Vaporisation is the energy required to change 1kg of a substance from a liquid state to a gaseous state without changing its temperature.

Question 19

What is the equation for the energy required to melt and boil?

Answer 19

Energy required to melt:
E = M x L
energy for a change in state = mass x specific latent heat of fusion

Energy required to boil:
E = M x L
energy for a change in state = mass x specifc latent heat of vaporisation

Question 20

What happens to temperature of a substance as energy increases? (heating curve)

Answer 20

As energy of a solid increases, the vibration KE of the particles increases. Once a certain temperature is reached, the solid melts, as bonds between the particles in a solid are melting. KE is not changing due to no change in temperature.
Once the entire substance is a liquid, temperature increases again as there is an increased KE of particles.
When a certain temperature is reached, the liquid vaporises. Whilst the substance is a mixture of liquids and gases, the bonds between the particles are being broken in the liquid. Energy is still being gained, though it’s not KE (it’s PE).
Once the substance is entirely a gas, the temperature increases again as there is an increased KE of particles.
Energy (or time) has been increasing the entire time.

Question 21

What happens to internal energy, thermal energy and potential energy as energy in a substance increases?

Answer 21

Temperature: increases/rises when it’s not changing state.
Internal energy: always rises as it is the total of KE + PE
Thermal energy: rises when it’s not changing state
Potential energy: Potential energy rises when it is changing state.
Potential energy is due to breaking and making bonds, kinetic energy is due to random thermal motion

Question 22

What is a cooling curve?

Answer 22

The opposite of a heating curve

Question 23

What is the difference between specific heat capacity and specific latent heat?

Answer 23

Specifc heat capacity determines the energy needed to change temperature, whilst specific latent heat is the energy needed to change state.

Question 24

What is temperature?

Answer 24

Temperature measures the average kinetic energy per particle of random thermal motion of the particle in an object (aka the average KE of the molecules)

Question 25

What is heat energy?

Answer 25

Heat energy is the total kinetic energy of random thermal motion of all the particles in an object.

Question 26

Silly Susie says that “molecules in a gas just stay in the smale place in the air all the time”. Please correct Silly Susie’s statement.

Answer 26

The molecules of a gas are in constant random motion.

Question 27

If you increase the temperature of a gas at a constant volume, what happens to the pressure of the gas?

Answer 27

If a gas is held at a constant volume, the pressure of a gas will increase if the temperature increases.

Question 28

What does Boyle’s law state?

Answer 28

Boyle’s law states that for a fixed mass of gas at a constant temperature the pressue of the gas is inversely proprotional to its volume.
So pressure x volume = constant
or P1 x V2 = P2 x V2

Question 29

Why and how does a gas exert pressure?

Answer 29

Molecules moving randomly constantly hit the container walls and bounce off.
In each collision the partile exerts a force on the container walls.
That’s why gases exert a pressure: the particles keep hitting the walls.
The more often they hit, and the harder they hit, the greater the pressure.
There is an increase in pressure if the volume is smaller, as they’re closer together.
There is an increase in pressure the higher the temperature, as they’re moving faster.

Question 30

What is the unit of pressure?

Answer 30

Pascals, Pa

Question 31

A gas can be compressed or expanded by pressure changes. The
pressure produces a net force at right angles to the wall of the gas
container (or any surface).

Question 32

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.

Answer 32

at

Question 33

What happens if you heat a gas in a rigid container?

Answer 33

Heating a gas at a constant volume increases its pressure because the individual collisions between the particeles and the container walls exert more force and they’re more frequent.
The particles are moving faster because they’ve gained kinetic energy.

Question 34

What happens if you compress a gas quickly/in a thermally insulated container? Like in a bicycle pump.

Answer 34

Boyle’s law doesn’t apply, because the gas will be either thermally insulated so the heat energy can’t get in or out or the gas will get compressed quickly enough so that there is no time for the heat energy to leave.
Compressing a gas quickly increases the thermal energy of the gas, therefore increasing its temperature.