kinetic particle model of matter

kinetic particle model of matter

• the kinetic particle model of matter states that all matter is made up of tiny particles which are in continuous and random motion

solids

at particle level

• arrangement

  • particles are closely packed and are arranged in a regular pattern

  • particles have the least energy among the three states of matter

• motion

  • particles vibrate about their fixed positions

  • held in position by strong attractive forces between the particles

observable properties

• solids have the highest densities

• have a fixed volume and fixed shape

liquids

at particle level

• arrangement

  • slightly less closely packed than in solids and are arranged in a irregular pattern

• motion

  • particles slide over each other throughout the liquid without fixed positions

  • the forces holding the particles together are weaker than in a solid

observable properties

• liquids have a slightly lower density than solids

• have a fixed volume but no fixed shape

gases

at particle level

• arrangement

  • particles are very far apart from one another and arranged in an irregular pattern

  • particles in gases have the most energy among the three states of matter

• motion

  • particles can move freely in any direction

  • the attractive forces between the particles are weak

observable properties

• gases have the lowest densities

• no fixed volume and no fixed shape

brownian motion

• refers to the continuous, random motion of particles suspended in a liquid or gas, as a result of bombardment by fast moving liquid or gas particles

• since we cannot see air particle, they are presumably very small

• to cause brownian motion of the smoke particles, air particles must be moving continuously, in random directions and at high speeds when they bombard the smoke particles

• brownian motion experiment thus serves as evidence for the random movement of molecules in a liquid or gas

objective

• to study the random motion (brownian motion) of smoke particles

apparatus

• microscope

• torchlight

• glass cell containing smoke

procedure

1. set up the apparatus

2. seal a glass cell containing some smoke and place it under the microscope

3. focus the microscope such that the smoke particles in the glass cell appear as bright spots. the smoke particles appear as bright spots because they reflect/scatter the light that shines on them

4. observe the motion of smoke particles

observations

• the smoke particles move about in a continuous, random manner

• the larger the smoke particles, the less agitated the motion

explanation

• random motion is due to the constant, uneven bombardment of the smoke particles by the invisible air particles

temperature

• temperature increases with the average kinetic energy of the particles in a body and vice versa

  • temperature in air increases

  • average kinetic energy of air molecules increases

  • air molecules bombard the smoke particles more forcefully and frequently

  • smoke particles move at higher average speed and change direction more frequently

pressure

• when a gas particle collides with the inner wall of the container, a force is exerted on the wall

• by considering numerous such collisions between the gas particles and the wall

  • an average force is exerted by the particles on the wall

  • the force per unit area gives rise to the pressure exerted by the particles on the wall

how can gas pressure in a container be increased/decreased

• consider

  • more/less frequent collisions

  • more forceful collisions

• at constant volume, when the temperature increases, the average speed of the particles increases, hence the particles will collide with the walls of the container more frequently and forcefully

• at constant temperature, when the volume increases, the particles will collide with the walls of the container less frequently