The Kinetic Molecular Theory and Gases
6 Postulates :
1) All matter is made up of tiny particles .
Importance: State isn’t relevant to particle size, just the space between them. For a gas, it’s large.
2) Particles are in constant motion. The higher the temperature, the more kinetic motion.
Importance : Gases have more energy and thus more space between the particles.
3) Particles have attraction & repulsion. When they approach they attract until they touch & repel.
Importance : Gas particles have large spaces and this force is usually small.
4) In the gaseous state particles occupy little volume over great space.
5) The forces of attraction between gas particles are very small.
6) Particles are elastic, no energy is released or absorbed upon collision.
Importance : reactions are difficult to occur in the gaseous state.
Pressure :
Definition: A force being exerted over a certain area
Pressure increases when: more force is being applied in the same area
The same force is being applied to an area that is decreasing
Gas pressure: the force of a continual bombardment of particles against the surface of the container.
Units : Pascals Pa
1 Pa = 1 N/m2
Average pressure : 101.3 kPa = 100 bar = 1 atm = 776 mm of Hg
WE WILL COMMONLY USE kPa
Instruments : Barometer – measures the air pressure in any of the 4 units
GAS LAW # 1 – Boyle’s Law – Volume and Pressure
Boyle first performed a series of experiments on gases in the mid 1600’s. He kept constant the temperature and the number of moles, but varied the volume and pressure to study their relationship. He found the following data: (graph this on graph paper for tomorrow)
Pressure in KPa (Independent Variable – y axis) / Volume in Liters (Dependent Variable – x axis)120 / 0.261
145 / 0.218
162 / 0.193
180 / 0.171
200 / 0.159
216 / 0.145
240 / 0.130
258 / 0.120
We will analyze this graph tomorrow and look at the relationship to solve problems.