Lesson 3 : Particle model of Matter

Density equation

Density = mass/volume (p = m/v)

Unit of density

kg/m³

Solid -> liquid

melting

Liquid -> solid

Freezing/ solidifying

Liquid -> gas

Boiling - at boiling point

Evaporation - any temperature

Gas -> liquid

condensation

Solid -> gas

Sublimation

Gas -> solid

Deposition

A change of state is a _____ change

Physical

Arrangement, movement and relative density of particles in a solid

1. Atoms (or molecules) are packed together in a regular structure

2. The atoms cannot move due to their fixed positions, but can vibrate

3. It is difficult to change the shape of a solid

4. High density due to large number of particles within certain volume

Arrangement, movement and relative density of particles in a liquid

1. Atoms are close together but are in an irregular arrangement.

2. Atoms can slide past each other randomly, and can flow and change shape to fit any container,

3. Because atoms are close together, it is very difficult to compress a liquid.

4. Medium to high density

Arrangement, movement and relative density of particles in a gas

1. Atoms or molecules are separated by relatively large distances and have a random arrangement

2. Atoms in a gas are are constantly in motion and move rapidly in random directions

3. A gas can expand to fit any volume

4. Very low density

Explain how to measure the density of an irregular object

1. Measure the mass of the object (before getting it wet!!!)

2. Using string, Submerge the object in water inside a filled EUREKA/ DISPLACEMENT CAN and collect the displaced water in a measuring cylinder

3. Measure the volume (get on eye level to avoid parallax error) and calculate density using p = m/v

Define Internal energy

The sum of the total kinetic (due to their motion) and potential energy (due to their positions/ bonds) of all the particles [only one can change at a time]

When a system is heated, what two things can happen to the internal energy?

1. Kinetic energy increases -> temperature rise

2. Potential energy increases -> change of state

(Only one can change at a time!!!!)

Why does, when a substance changes state, mass is conserved?

Mass is conserved because the total number of particles remains exactly the same, as it is a physical change.

Why does the temperature remain constant on a heating graph during a change of state?

Thermal energy provided is being used to break or weaken the intermolecular forces (increasing potential energy) rather than increase the speed of the particles (kinetic energy)

Define specific heat capacity

The amount of energy required to raise the temperature of 1kg of a substance by 1C

Unit of specific heat capacity

J/kg°C

Define specific latent heat

The amount of energy required to change the state of 1kg of a substance without a change in temperature

Unit of specific latent heat

J/kg

Differentiate between the latent heat of fusion and the latent heat if vaporisation

1. Fusion - energy required to change state between a solid and a liquid

2. Vaporisation - energy required to change state between a liquid and a gas

Explain how a gas exerts pressure on the walls of it's container

As they collide with the walls of the container, they exert a force at right angles to the surface

Explain how the motion of molecules in a gas is related to both its temperature and pressure

Higher temperature increases the average kinetic energy and therefore speed of the gas particles, increasing the frequency and force of collisions, increasing total pressure.

Explain qualitatively the relation between the temperature of a gas and its pressure at a constant volume

As the temperature increases, at a constant volume the pressure increases, as they have more kinetic energy and therefore hit the walls of the container more frequently and with more force, increasing the pressure

Unit of pressure

Pascal (Pa)

Unit of volume

m^3

State the relationship between pressure and volume for a fixed mass of gas at constant temperature

They are inversely proportional (pV = constant - Boyle's law)

Why does doing work on a gas (eg: compressing it quickly with a pump) cause its temperature rise?

Doing work transfers energy to the gas particles, increasing their internal energy, increase the kinetic energy of particles, therefore causing the temperature to rise