STATES OF MATTER

Matter can exist in three states,  that is, solid, liquid and gaseous The fundermental difference between these three is the forces of attraction (cohesive forces) between the particles, 

SOLID( strong cohesive forces)	LIQUID(weak cohesive forces)	GASES
Have definite shape and volume	Have no definite shape but definite volume	Have no definite shape and volume
Very dense	Less dense	Least dense
Incompressible	cannot be compressed	Compressible
Fixed mass	Substances have a fixed mass	Fixed mass
Particle vibrate and rotate about a fixed point	Particles can vibrate as well as  move about within a restricted space	Particles move about constantly at great speed and at random

      

CHANGE OF STATE

MELTING

Melting is the physical process where a substance changes from a solid to a liquid. When a solid is heated, the particles acquire greater kinetic energy and move violently. A point is reached when the forces of vibration overcome the cohesive forces holding the solid particles together and the crystalline structure collapses. The particles are no longer held in fixed positions but are free to move about and the liquid state is reached. The temperature at which this occurs is called the melting point of the solid.

 

BOILING

When a liquid is heated, the rate of evaporation increases and the value of the saturated vapour pressure equal the prevailing atmospheric pressure. When this happens, the liquid is said to boil and the temperature at which this happen is known as the boiling point of the liquid.

The boiling point of a liquid change with change in atmospheric pressure. If the pressure is raised, the boiling point will increase and if the pressure is lowered the boiling point will decrease. Also, the presence of impurities increases the boiling point of a liquid.

EVAPORATION

Evaporation is the process of vapourization of liquids at all temperatures. When the surface of a liquid is exposed, the molecules near the surface of the liquid will acquire extra kinetic energy, large enough to enable them break away from the cohesive force binding them to the neighbouring particles. Once free, they escape from the liquid surface to become molecules in the vapour state.

 

Evaporation results in decrease in the volume of liquid and lowering the temperature of the liquid, therefore it causes cooling. Also, it occurs at all temperature but increases with increase in temperature. In addition, it is slower in electrovalent liquids than in covalent liquids.

 

DIFFERENCES BETWWEEN EVAPORATION AND BOILING

EVAPORATION	BOILING
Takes place at the surface of the liquid	Involves the entire volume of the liquid
Takes place at all temperature	Takes place at a fixed temperature

 

CONDENSATION AND FREEZING

Condensation is a process whereby a vapour loses some of its kinetic energy to a colder body and changes into the liquid state.

When a liquid cools, it loses heat energy to its surroundings, causing its temperature to drop. If the cooling continues, the temperature of the liquid keeps dropping until it reaches the freezing point of the liquid. At this temperature, the liquid changes into solid.

 

EVALUATION

1.     Describe the melting process of a solid.

2.     State two differences between evaporation and boiling.

 

KINETIC THEORY OF GASES

The theorypostulates the following for an ideal or perfect gas:

Gas molecules are in constant, rapid, straight motion, colliding with one another and with the walls of the container.

 

The collision of gas molecules is perfectly elastic.

The total volume of the gas molecule is negligible compared to the volume of the container.

The force of attraction between the gas molecules is negligible.

The average kinetic energy of the molecule is a measure of the temperature of the gas molecules.

 

PHENOMENA SUPPORTING THE KINETIC THEORY OF GASES

Brownian motion: This is the constant, irregular movement of particles in a liquid or gas. It shows that gas molecules are in constant motion.

Diffusion: Diffusion is the movement of particles from a region of higher concentration to lower concentration. Diffusion is common in gases and it results from the random movement of particles of a gas.