P3 Particle Model of Matter

Three states of matter

• Solid (e.g ice)
• Liquid (e.g water)
• Gas (e.g. water vapour)

The particle model is widely used to predict the behaviour of solids, liquids and gases and this has many applications in everyday life.It helps us to explain a wide range of observations and engineers use these principles when designing vessels to withstand high pressures and temperatures such as submarines and spacecraft. It also explains why it is difficult to make a good cup of tea high up a mountain!

• Particles of a certain material are always the same, no matter what state it is in
• But particles have different amounts of energy in different states
• and the forces between particles are different in each state, and are arranged differently

Solids

• space - minimal/no space between the particles
• movement - vibrate around a fixed point
• shape - don't change shape/fixed shape
• volume - has a fixed volume
• forces - strong forces between the particles

Liquids

• space - has minimal gaps
• movement - slide and flow past eachother
• shape - changes shape according to the container 
• volume - has a fixed volume
• forces - medium forces between the particles

Gases

• space - large gaps between particles
• movement - random directions at varying speed
• shape - changes shape freely around the container
• volume - doesn't have a fixed volume
• forces - weak/no forces between the particles 

The molecules of a gas are in constant random motion.The temperature of the gas is related to the average kinetic energy of the molecules.

The higher the temperature the greater the average kinetic energy and so the faster the average speed of the molecules. When the molecules collide with the wall of their container they exert a force on the wall.

The total force exerted by all of the molecules inside the container on a unit area of the walls is the gas pressure. Changing the temperature of a gas, held at constant volume, changes the pressure exerted by the gas

Density relates to the mass of an object and how tightly packed the particles are.  It is the mass per unit volume.  density = mass/volume

Formula      density equation= ρ (kg/m^3) = m(kg) / v(m^3)

A dense material has particles that ae closely packed together. So solids are generally more dense than liquids and liquids are generally denser than gases.

Measuring density

1) use a balance to measure the object's mass
2) if it is a regular solid, measure the length, width and height with a ruler then multiply together to find the volume
3) if the solid is irregular, you can use the displacement method. fill a eureka can with water, submerge the object in it, and collect the water in a measuring cylinder. the total water that is displaced is the object's volume.
4) convert any values into the correct units, and find the density by using the abve equation mass/volume

Internal energy is caused by two things:

• the amount of kinetic energy particles have depending on their individual motion
• the potential energy particles have due to molecular attraction

heating a system causes transfers energy to its particles (they gain energy in their kinetic stores so move faster) which increases the internal energy.  This leads to a change in temperature, or a change in state.

Change of state - physical chnage not chemical MEANS DONT END UP WITH NEW SUBSTANCE.  REVERSING A CHANGE IN STATE SUBSTANCE WILL RETURN TO ORIGINAL STATE 

MASS IS CONSERVED AS NUMBER OF PARTCILES DONT CHNAGE ONLY ARRANGEMENT OF PARTICLE

SOLIDS-

MELTING-liquid

SUBLIMATION-gas

LIQUIDS-

FREEZING-solids

BOILING AND EVAPORATING-GAS

GAS-

CONDENSING-liquid

WHEN MELTING OR BOILING A SUBSTANCE YOU ARE OUTTING ENERGY IN WHICH IS INCREASING THE INTERNAL ENERGY

ENERGY IS USED FOR BREAKING INTERMOLECULAR BONDS NOT RAISING TEMPERTAURE WHEN CONDENSING OR FREEZING BONDS ARE FORMING BETWEEN PARTCLES WHICH RELEASES ENERGY 

when the temperature of a system changes, the size of that change depends on the mass of the substance, its specific heat capacity (what it is made of) and the energy input.

a change in state occurs when the particles have enough energy from being heated in their kinetic energy stores to break the bonds between them.

remember: the specific heat capacity of a substance is the amount of energy required to raise the temperature of 1kg of that substance by 1°C.

energy = mass * SHC * temp change

E (J) = m (Kg) * C (J/Kg°C) * θ (°C)

the temperature of a substance doesn't change while it is changing state because the energy that is being transferred is being used to change the state.

the specific latent heat of a substance tells us how much energy is needed to change the state of 1Kg of a substance at a constant temperature.

specific latent heat of fusion = solids --> liquids

specific latent heat of vaporisation = liquids --> gases

energy (J) = mass (Kg) * SLH (J/Kg)