Molecular kinetic theory model

What is the scientific distinction between the gas laws and kinetic theory?

The gas laws are empirical which means they are based on observation and evidence, kinetic theory is based on assumptions and derivations from existing theories.

What is the internal energy of an ideal gas?

U (internal energy)= N (number of particles in ideal gas) * Ek ( average kinetic energy of a single particle)

ideal gas molecules have no intermolecular forces, so they have no potential energy only kinetic. temperature is proportional to average Ek, therefore for an ideal gas internal energy is proportional to temperature.

What is the kinetic theory?

a model used to describe gases as being made of many tiny particles that are in constant, random motion. It links the microscopic properties of particles (mas, speed) to macroscopic properties of particles (particles and volume)

What assumptions is the kinetic theory made of?

• Molecules of a gas behave as identical

• molecules of gas are hard, perfectly elastic spheres

• volume of molecules is negligible compared to volume of container

• time of a collision is negligible compared to the time between collisions

• there are no intermolecular forces between molecules

• external forces are ignored

• molecules move in continous random motion

• newtons laws apply

• there are a very large number of molecules

What is the kinetic theory model equation?

pV= 1/3 Nm (c rms)²

p= pressure (Pa)

V= volume (m³)

N= number of molecules

m= mass of one molecule of gas (kg)

c rms = root mean square speed of molecules (ms-¹)

What is the equation for the average kinetic energy of one molecule of gas?

Ek= ½ m(c rms)²= 3/2 kT= 3RT/2NA

What is Brownian motion?

A phenomenon when small particles ( pollen or smoke etc) suspended in a liquid or gas are observed to move around in random, erratic fashion. It can be observed under a microscope and provides evidence for the existence of atoms in a gas or liquid.

What are the features of Brownian motion?

Particles have a range of speeds and no preferred direction of movement. The observable particles in Brownian motion are significantly bigger than the molecules that cause the motion. The collisions cause larger particles to change their speed and direction randomly. The atoms are able to affect the larger particles in this way because they are travelling at a speed much higher than the larger particles, they have a lot of momentum, which they transfer to the larger particles when they collide.