Second Term Lesson Note for Week Eight
Class : SSS 1
Subject : Chemistry
Topic : Kinetic Theory Matter
Duration : 40 Minutes
Period : Single Period
Reference Book :
Instructional Material :
Learning Objectives : By the end of the lesson learners will be able to :
i. Explain the kinetic Theory of gases.
ii. Define Osmosis and Diffusion
iii. Identify the phenomenon supporting kinetic Theory of gases.
Content :
KINETIC THEORY OF GASES
The gas laws, which explain the physical behaviour of gases can be explained by the kinetic theory of gases. This states that:
The gas molecules move randomly in straight lines, colliding with one another and with the wall of the container.
Example: if a bottle of perfume is opened, the smell is quickly detected everywhere.
The collision of gas molecules are perfectly elastic i.e. when the molecules collide with the wall of the container, they re-bounce like elastic balls without any loss of energy.
The actual volume occupied by the gas molecules themselves is negligible i.e. the gas molecules are so small when compared with the volume of the container or distances between them.
The cohesive forces between the gas molecules are negligible
The temperature of the gas is a measure of the average kinetic energy of the gas particles
NOTE: the theory describes the behavior of an ideal gas, but not everything is true about real gas
PRESSURE EXERTED BY GASES
Gas particles collide with each other and with the walls of the containers.
Each time it happens, the gas exerts a very small force on the walls.
This force per unit area is called gas pressure. It is constant.
The gas pressure is measured in;
Atmosphere (atm) or Millimetre mercury (mmHg) or Pascal (Nm -²)
Relationship between the units
1 atm = 760mmHg = 101325 Nm-²
SUMMARY OF KINETIC THEORY OF MATTER
Particles of matter are continually moving in a random motion so posses kinetic energy.
Using the Kinetic Theory to define the physical states of matter:
Solid – a substance whose particles have a low kinetic energy. The particles of a solid are held close together by intermolecular forces of attraction. Because the particles are so close together, they appear to vibrate around a fixed point.
When the temperature of a solid is raised, the velocity of the particles increases. The collisions between the particles occur with greater force, causing the particles to more farther apart. The ordered arrangement of the solid breaks down and a change in physical state occurs.
Liquid – a substance whose particles have enough kinetic energy to stretch the intermolecular forces of attraction. Collisions between the particles a strong enough to force the particles apart. The particles appear to have a moving vibration because they are still under the influence of the intermolecular forces of attraction.
As the temperature of a liquid is raised, the velocity of the particles increases. The collisions eventually become so great that the particles break all intermolecular forces, begin moving independently between collisions, and a change in physical state occurs.
Gas – a substance whose particles have enough kinetic energy to break all intermolecular forces of attraction. The particles of a gas move independently of each other. The particles move at random because they have overcome the intermolecular forces of attraction.
When a gas is raised to extreme temperatures, over 5000 °C, they have so much kinetic energy that their collisions will break electrons out of the atoms, and a change in physical state occurs.
Plasma – a charged gas. The particle collisions are violent enough to break electrons out of the atoms, producing particles with charges (electrons and positive ions).
Because of its extreme temperature, plasma is not common on Earth. Wet-lab chemistry is not concerned with plasma and its characteristics.
Physical state at room temperature (25°C) and standard atmospheric pressure:
Under these conditions, the physical state of a substance is determined mainly by its chemical bond characteristics.
Ionic compounds have strong electric charges holding the ions together as solids.
Nonpolar molecular compounds of low molecular mass tend to be gases.
Greater molecular mass and greater polarity both tend to make substances more dense, producing either liquid or solid.
Intermolecular forces of attraction:
Within an atom, these forces are called weak forces, because they are much weaker than chemical bonds between atoms. Weak forces involve the attraction of the electrons of one atom for the protons of another atom.
When these forces interact between molecules, they are known as van der Waals forces.
PHENOMENA SUPPORTING KINETIC THEORY
Nobody has seen the tiny particles that make up matter but scientist carried out
some work and ascertain that the particles are in constant motion
The motion can be proved as follows:
Brownian movement
By Brown (a botanist in 1827)
He dropped a pollen grain in a drop of water and examined it under
Observation: There was irregular movement of the grain (zigzag)
Conclusion: Movement was caused by the bombardment of the
pollen grains by the water molecules
Brownian movement
Diffusion
Movement of solute particles through a medium from a medium of higher concentration to a region of lower concentration.
Diffusion in Gases
Fastest (in seconds)
Particles have more kinetic energy
Rate of diffusion is affected by the densities of the gases.
NOTE
NH3 gas diffuses faster than HCl because it is lighter than HCl.
The evidence of the above statement is that NH3 travels at one third of the tube (distance A) faster than HCl (distance B) i.e. A > B.
The molecular masses of the gases are used to determine the lighter gas i.e. the lower the molecular mass the faster the rate of diffusion. But where the molecular masses are equal, the 2 gasses diffuse at the same rate.
NOTE:d1and d2 stands for distance
Diffusion of Liquids
slower than gasses (in minutes/hours)
particles have less K.E
….
.
Note
the fine jets acts as the boundary in the beginning.
The blue CuSO4 solution spreads upwards, against gravity. Therefore, it liquids overcome the force of gravity.
Diffusion in Solids.
Slowest ( in years )
Particles have least K.E
Osmosis
Special case of diffusion which involves the movement of water molecules
Osmosis is the movement of water molecules, through a semi permeable membrane, from the region where they are in higher concentration to the region where they are in lower concentration.
Example: place some dried bean seed in a beaker of water and leave for some time.
Observation: The bean seed swell up
Result: water molecules have moved through the skin of the seed (semi-permeable) into the seeds by osmosis.
EVALUATION
1. The escape of molecules with more than average kinetic energy of the molecule
(A).melting (B).freezing (C).evaporation (D).efflorescence
2. The phenomenon whereby the atmospheric pressure equals the saturated vapour pressure is called
(A).freezing (B).latent heat (C).boiling (D).normal pressure
3. Using the kinetic theory of matter, describe the nature of the following states of matter.
4. State the kinetic theory of matter and outline 3 natural phenomena which support it.
CONCLUSION : The teacher summarizes the lesson by explaining all over again for a better understanding.