p1 particle model of matter

describe solids

Particles are very close together

Arranged in regular pattern

Vibrate but do not move from place to place

Describe liquid

Particles are close together

Not arranged in regular pattern

Also can move around each other

Gas

Very far apart

Particles not arranged in any pattern

Moving very rapidly

Which is gas

Which is liquid

Which is solid

What is density ?

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

An example of density

The brick has high density it has lots of mass packed into its volume

The polystyrene block has a low density it has a lower mass packed into its volume

What is the equation for density

Explaining the density of different materials

Solids usually have a vey high density Bc the particles are packed closely together solids have a lot of mass for their volume

Liquids usually have a high density bc the particles are close together liquids have a lot of mass for their volume

Gases have low density bc the particles are very apart so gases have a small mass for their volume

Polystyrene is a exception for these rules

It’s a solid but it has low density bc it has a very open structure and is full of air spaces it has a small mass for its volume.

What do all 3 particles have in common

Kinetic

Potential energy (intermolecular forces and chemical bonds )- forces

Wat is internal energy

Is the energy stored in a system by the particles

Is the total kinetic energy and potential energy of all the particles (atoms and molecules that make up a system

What happens when we heat a solid?

We increase the internal energy at some point the solid turns to liquid (melting )

What happens if we Continue to heat liquid ?

We increase the internal energy at some point the liquid will turn to a gas that is boiling

What happens if we cool the gas down?

Then we reduce the internal energy at some point the gas turns back to liquid (condensation )

What happens if we cool liquid even more ?

We reduce internal energy even more and then liquid turns to solid - freezing

Whats it called when a solid turns to gas

Sublimation

What happens when changes of state take place

Mass is always conserved were not adding or taking away any particles

Changes of state are

Physical change not chemical

If we reverse the change the material recovers its original properties

What is evaporation

When a liquid turns to gas but only on the surface of a liquid

In this case only the particles on the surface have enough energy to turn into gas

Specific heat capacity

Example - how much energy is stored in hot water ?

To answer this we need to look at the idea of specie heat capacity

What is specific heat capacity

Of a substance

Is the amount of energy required to raise the temperature of 1kg of the substance by 1 degree

What is the equation for specific heat capacity

Heating graph 1 parts

The temperature of the solid is rising as we are increasing the energy of the particles

At some point the tem stops rising and the line is now horizontal at this point the solid is changing state and turning in to liquid by melting

The energy we are putting in is weakening or breaking the forces of attraction between the particles allowing substance to change from a solid to liquid scientists call the energy needed for a substance to change state the latent heat

Heating graph2 part

During the change of state we are increasing the internal energy store of the system but we are not changing the tem

The tem that the substance melts at is the boiling point

Eventually alll of the solid will have melted into a liquid and now the tem starts to rise again bc we are increasing the energy of the particles

Heating graph part 3

Tem stops increasing and line becomes horizontal again

The substance is now boiling the energy we are putting in is weakening or breaking the forces of attraction between the particles allowing substance

Once al the liquid has boiled the tem starts to rise again

Cooling graph

The energy needed for. Substance to change state it the latent heat this is ..

The specific latent heat of a substance is the amount of energy required to change the state of one kilogram of the substance with no change in tem

Specific latent heat example is ice if we wanted to melt 1kg of ice

The energy it would take ..

334 000 J of energy to melt one kilogram of ice scientists call this the specific latent heat of fusion

What is specific latent heat of fusion

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

What if we wanted to change a substance from a liquid to gas how much energy would that take

This is called specific latent heat of vaporisation

• the energy required to change 1kg of a substance from a liquid to vapour with no change in tem

We can use the idea of Specific latent heat To calculate energy change when a change of state takes pace calculation

Gas pressure

The pressure of a gas is due to the particles colliding with the walls of the container that the glass is held in

By colliding with the walls of the container the gas particles are exerting a pressure

We can increase the pressure if we increase the number of Collisions per second or the energy of each collision One way to do that is to increase the tem of the gas

Gas pressure 2

The tem of a gas is related to the average kinetic energy of the particles

Gas pressure 3

At low tem particles have lower kinetic energy there are fewer collisions per second these are lower energy collisions

So low tem - low pressure

At high tem particles have higher kinetic energy there are more collisions per second these are higher energy collisions

High tem particles- high pressure