PhysicsKinetic Particle Theory

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What is Matter?● Matter is anything that has mass and occupies space● Matter can exist in 3 states: solid, liquid, gas

Solid Liquid GasHas definite volume Has definite volume No definite volume as it

entirely fills its container

Has definite shape No definite shape, takes the shape of its container

No definite shape, takes the shape of the whole container

Usually hard and rigid Can flow Can flowNot compressible Not compressible Compressible

Kinetic Theory of Matter● To explain why the 3 states of matter behave the way

they do● Based on the following assumptions

○ All matter is made up of a large number of small particles - atoms or molecules

○ The small particles are always in continuous random motion or vibration

○ The higher the temperature, the faster the particles move○ The inter-particle collisions are perfectly elastic - means

that both the kinetic energy and momentum are conserved in the collisions

Kinetic Theory of Matter● The continuous random motion of the particles in the

different states of matter is shown by Brownian motion and diffusion

● Brownian motion is the random motion of gaseous and liquid molecules

Random motion of particles

Kinetic Theory of Matter● Diffusion is the process by which

different kinds of matter in the same or different states mix with one another due to the random movements of the particles in the matter

● Diffusion occurs fastest in gases and slowest in solids

● Factors affecting diffusion rate○ Rate of diffusion increase with

temperature○ Rate of diffusion is inversely

proportional to the square root of its density

Solid, Liquid, Gas

Molecular model of the 3 states of matter

Solids Liquids Gases

Solid molecules arranges in a regular pattern known as a lattice(definite shape and volume)

Liquid molecules are not arranged in any particular pattern(no definite shape)

Gas molecules are not arranged in any particular pattern(no definite shape)

The attractive intermolecular forces are very strong and are able to hold molecules in fixed positions

The weaker intermolecular forces cannot hold molecules in fixed positions. Molecules move among one another (can flow)

The intermolecular forces are negligible so molecules can move freely (can flow easily and completely fill the container)

Molecules are very close to one another (not compressible)

Molecules are slightly further away from one another than in solids (not compressible)

Molecules are very far apart from one another. They can easily move closer to one another (easily compressible)

Molecules only vibrate about their fixed positions (cannot flow and diffuse slowly)

Molecules rotate and translate randomly (can flow and diffuse faster)

Molecules rotate and translate randomly and freely (can flow and diffuse faster than liquids)

Change of States

Pressure-Volume relationship of a gas

● Randomly moving gas particles collide with one another and with the inner walls of the container

● The collisions produce forces● The force acting on each unit of the inner walls is the gas

pressure exerted on it● When the volume of gas is halved by halving the volume of

its container, the number of molecules per unit volume in the container will be doubled.

● The number of collisions between the gas molecules and the inner walls will double the force produced

● Hence, the force acting on each unit area of the inner walls (gas pressure) will be doubled

Boyle’s Law● This relationship between pressure and volume of a

gas at constant temperature and fixed mass is stated in Boyle’s Law:○ For a fixed mass of gas at constant temperature, the

pressure is inversely proportional to its volume.

Example QuestionA tyre contains 1500cm3 of air at pressure p. The volume of air in the pump is 500cm3 at the same pressure p. what will be the pressure in the tyre after one stroke of the pump, assuming the volume of the tyre and the temperature of the air do not change?

Solution

p1: original pressure of airp2: pressure of air in the tyre after one stroke of the pumpv1: total volume of air in the tyre and pumpv2: volume of air in the tyre after one stroke of the pump

p1 x (1500 + 500) = p2 x 1500p2 = 4/3p1