P6

Density

mass of a given volume of a substance

Density of water

1000kg/m³

Solids

• Particles with high density

• Regular patterns

• Vibrate around fixed positions

• Low energy

Liquids

• Particles with medium density

• Randomly arranged

• Move around each other

• Greater energy

Gases

• Particles with low density

• Randomly arranged

• Move quickly in all directions

• Highest energy

Measuring density of a regular object

• Place object on a top pan balance and note down its mass

• Use a Vernier Callipers to measure the object’s dimensions

• Repeat these measurements and take an average of the readings before calculating the density

• Calculate the volume depending on its shape

Measuring density of an irregular object

• Place object on top pan balance and note down its mass

• Fill eureka can with water up to a point just below the spout

• Place empty measuring cylinder below its spout

• Carefully lower object into eureka can

• Measure volume of water displaced in measuring cylinder

• Repeat these measurements and taken an average before calculating density

Density formula

Mass (kg)/Volume (cm³)

Mass during state changes

• Stays the same

• Has different volumes

Changes of states

• Physical changes

• This change can be reversed so the material can recover its original properties

Solid to liquid

melting

liquid to gas

evaporation

deposition

gas to solid

freezing

liquid to solid

solid to gas

sublimation

condensation

gas to liquid

internal energy

the energy stored in a system by the atoms and molecules that make up that system

Parts of internal energy

• Kinetic

• Potential

Increased heat on internal energy

the internal energy of the particles increases. This can result in the material changing state

temperature of an object depends on

• What it’s made out of

• Mass of object

• Amount of energy

Specific heat capacity

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

Specific heat capacity (J/Kg⁰C)

Energy change (J)/ Mass (kg) x Temperature change (∆θ)

Latent heat

energy needed to change the state of a substance without a change in temperature and energy supplied is used to change the internal energy store of the substance

Specific latent heat of fusion

Latent heat for melting

Specific latent heat of evaporating

specific latent heat of vaporisation

Specific latent heat of evaporating and vaporisation formula (J/Kg)

Energy (J)/Mass (kg)

Heating and cooling graphs

• As heat energy is added to a solid, the temperature rises until it reaches its melting point.

• As the substance melts, all the heat energy added is used to change the state of the substance with no temperature change.

• When all the substance is melted, the temperature will then rise until the boiling point is reached.

• Again, heat energy is now required to change the state to a gas with no temperature change.

Brownian motion

Molecules in a gas are in constant random motion

What happens to gas molecules if temperature gets increased

• temperature of this gas is related to the average kinetic energy of all the particles.

• If the temperature of the gas is increased, the particles will move faster

• Faster moving particles exert a greater force on the walls of the container.

• This will increase the amount of collisions

• This will either cause the container to expand (balloon) or increase the pressure of the gas

Relationship between pressure and temperature

Directly proportional as long as volume remains constant

What happens when a gas is compressed in a fixed container

• more particles in a given volume to strike the walls of the container

• therefore the pressure on the container walls increases

pressure produces a net force at right angles to the wall

means the pressure will act evenly in all directions.

What happens if you pull plunger back on a syringe

• Particles of gas will be occupying a greater volume of space

• Results in fewer collisions

• Therefore reduced pressure

Pressure and volume relationship

Inversely proportional

Formulas for pressure and volume

• PV = Constant

• P=1/V

• P₁V₁ = P₂V₂

Work done on a gas

energy is transferred to the gas by a force. This transfer of energy to the gas increases its temperature

Work done on a foot pump to inflate a tyre

• work is done by the piston on the vibrating air particles inside the pump.

• There is therefore a transfer of energy between the piston and the particles and this results in an increase in kinetic energy of the air particles.

• If the kinetic energy of the air particles increases then there will be more collisions between gas particles.

• This will cause the temperature of the gas to rise