Particle model of matter (paper 1-physics)

How are particles arranged in a solid and its density?

• High density

• Particles are tightly packed in a fixed,regular arrangement

• Lots of mass in a small volume → density is high

• Particles vibrate but do not move from place to place.

How are particles arrange in a liquid and its density ?

• Medium density

• Particles close together but not arrange in a regular pattern→ slightly more space between particles→ lower density than solids

• Particles can move around each other.

How are particles arrange in a gas and its density ?

• Lowest density

• Particles are very far apart and arranged in any pattern.→ move freely

• very little mass in a large volume → gases are much less dense

• Particles move rapidly.

Required practical :Density → how to determine the densities of regular & irregular solid objects

Regular objects → have dimensions easy to measure e.g: solid :

• Measure the mass using a balance . Then measure length, width, & height of object using a ruler

• Calculate volume using : Volume = L * W *H

• Use the density formula = Density = mass/volume

Irregular objects→ can’t measure its dimensions easily

• measure the ass using a balance.

• Find its volume using a displacement method : fill a eureka can with water just below the spout & place a measuring cylinder underneath - the volume of water displaced = volume of object

• Use the density formula again

Use consistent units → E.g: grams & cm3 / kg / m3

Calculating liquid:

• place measuring cylinder on a balance &zero the balance

• Pour 10ml of the liquid into measuring cylinder & record the total volume & mass → repeat process until measuring cylinder is full

• For each measurement use the formula to find the density

• Take an average of calculated densities to get an accurate value for the density of the liquid

What does density mean?

The mass of a given volume.

Formula for density

density= mass/volume

kg/m³ or g/cm³

Why does the solid polystyrene have a low density?

• It has a very open structure and is full of air spaces so it has a very small mass for it’s volume.

Internal energy

• The total energy stored inside a system due to its kinetic energy (Movement) and the Potential energy(intermolecular forces& chemical bonds)

• Energy stored inside a system by particles

Changes of state: Effect of heating & Cooling on internal energy

• Heat a solid → Increases internal energy → melting → into liquid

• Further heat →continues increasing internal energy → boiling state → into gas

• Cool gas→ reduces internal energy → condensation→ becomes liquid

• Cool further →reduce internal energy even more → freezing → becomes solid

• SUBLIMATION : solid → gas

• Mass is always conserved during changes of state → no gain/loss of particles

• Chanegs of state = physical changes → if reverse → recovers to original properties

• EVAPORATION : liquid → gas (only on surface particles )

What is specific heat capacity?

The amount of energy required to raise the temperature of 1kg of a substance by 1 degrees Celsius.

Formula for specific heat capacity

Q=m ×c×AT

Change in thermal energy (J)= mass (kg) × specific heat capacity (J/kg degrees Celsius) × temperature change (degrees Celsius)

Heating & cooling graphs

x-axis → time or energy added

Y-axis → temperature of the substance

Heating :

• Solid heating → temperature rises & particles move faster → reaches melting point = temperature constant plateau & energy breaks bond → temp. Stays same → until liquid heating → temperature rises & particles move even faster → reaches boiling point = hits plateau & energy breaks intermolecular forces→ gas heating → temp. Rises & particles moving faster

Cooling :

• Gas cooling → temperature decreases & particles move slower → condensation = temp. Constant plateau & energy released as bonds form →until liquid cooling → temp. Decreases again & particles slow down → reaches freezing point = constant plateau → temp stays constant & energy released as bonds form → solid cooling → temp. Falls as solids vibrate less

Why does temperature stay the same during the change of state?

• (When a change of state occurs, the internal energy increases but not the temperature.)

• This is because the energy is being used to weaken or break the forces of attraction between the particles.

REMEMBER: During flat plateaus (melting,boiling,freezing,condensing) , temperature stays constant while the state changes → energy is sued to break / for bonds , not change temperature

What is specific latent heat?

The amount of energy required to change the state of 1 kilogram of the substance with no change in temperature.

Specific latent heat of fusion

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

Specific latent heat of vaporisation

The energy required to change 1kg of a substance from a liquid to a gas with no change in temperature.

Specific latent heat formula

E= m × L

Energy for change of state (J) = mass (kg)× specific latent heat (J/kg)

Temperature & particle energy & gas pressure

Temperature & particle energy:

• Temperature measures the average kinetic energy of gas particles

• Higher temperature→ particles move faster

Temperature & pressure:

• increasing temperature→ particles hit container walls more often & with more force→ pressure increases (if volume constant)

• Decreasing temperature→ particles move slower→ pressure decreases