Physics: Topic 3: Particle model of matter

What is the equation for density?

p = m/v
density = mass / volume

What is density, p, measured in?

Kilograms per metre cubed - kg/m³

What is volume, V, measured in?

Metres cubed - m³

What can the particle model be used to explain?

• The different states of matter

• Differences in density

What are the 3 states of matter?

• Solid

• Liquid

• Gas

What is the density of a solid like?

Lower than liquids and gases - not much space between particles

What is the density of a liquid like?

Lower than gas, higher than solid - not much space between particles

What is the density of a gas like?

Higher than solid and liquid - lots of space between particles

What are the changes of state?

• Melting

• Freezing

• Boiling

• Evaporation

• Condensing

• Sublimation

What happens to the mass of a substance when it changes state?

It is conserved

What type of change is a change of state?

Physica;

Why do physical changes differ from chemical changes?

The material recovers its original properties if the change is reversed

What is internal energy?

The total kinetic energy and potential energy of all the particles that make up a system

What does heating do to the energy stored within the system?

Changes it by increasing the energy of the particles that make up the system

How can heating change the system?

• Raises the temperature

• OR produces a change of state

If the temperature of the system increases, what does this depend on?

• The mass of the substance heated

• The type of material

• The energy input to the system

What is the equation for change in thermal energy?

∆E  = m c  ∆θ

Change in thermal energy = mass x SHC

What is the specific heat capacity of a substance?

The amount of energy required to raise the temperature of one kilogram of the substance by one degree Celsius

What is latent heat?

The energy needed for a substance to change state

What happens when a change of state occurs?

The energy supplied changes the energy stored (internal energy), but not the temperature

What is the specific latent heat of a substance?

The amount of energy required to change the state of one kilogram of the substance with no change in temperature

What is the equation for specific latent heat?

E = m L

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

What is specific latent heat, L, measured in?

Joules per kilogram - J/kg

What is specific latent heat of fusion?

The change of state from solid to liquid

What is specific latent heat of vaporisation?

The change of state from liquid to vapour

What are molecules of a gas like?

In constant random motion

What is the temperature of a gas related to?

The average kinetic energy of the molecules

What does changing the temperature of a gas, held at constant volume also change?

The pressure exerted by the gas

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

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

What can pressure changes do to a gas?

Expand or compress it

What does pressure produce?

A net force at right angles to the wall of the gas container/ any surface

Students should be able to use the particle model to explain how increasing the volume in which a gas is contained, at constant temperature, can lead to a decrease in pressure

For a fixed mass of gas held at a constant temp…

pV = constant

pressure x volume = constant

What is pressure, p, measured in?

Pascals - Pa

What is work?

The transfer of energy by a force

What does doing work on a gas do?

Increases the internal energy of the gas and can cause an increase in the temperature of the gas

Students should be able to explain how, in a given situation eg a bicycle pump, doing work on an enclosed gas leads to an increase in the temperature of the gas