kinetic model of matter Flashcards
Matter can exist in one of three different states:
solid, liquid, gas
the temperature of a substance is a measure of the
kinetic energy present of its particles
the quicker the p. move the greater the temperature
properties of solids, liquids and gases in terms of shape and volume
Solids
Solids have a definite shape (they are rigid).
Solids have a definite volume.
Liquids
Liquids have no definite shape – they are able to flow, and will take the shape of a container.
Liquids have a definite volume.
Gases
Gases have no definite shape – they will take the shape of their container.
Gases have no fixed volume – if placed in an evacuated container they will expand to fill the container. They are also highly compressible.
properties of solids, liquids and gases in terms of
arrangement and motion of molecules
In a solid:
The molecules are very close together and arranged in a regular pattern.
The molecules vibrate about fixed positions.
In a liquid:
The molecules are still close together (no gaps) but are no longer arranged in a regular pattern.
The molecules are able to slide past each other.
In a gas:
The molecules are widely separated – about 10 times further apart in each direction.
The molecules move about randomly at high speeds.
properties of solids, liquids and gases in terms of
forces and distance between molecules
In a solid:
The molecules are held in place by strong intermolecular bonds.
These bonds prevent the molecules from moving, giving the solid its rigid shape and fixed volume.
In a liquid:
The molecules have enough energy that they are able to break the bonds between them.
The bonds are still there, but they no longer hold the molecules in place.
As a result, the molecules can move around (by sliding past each other) allowing the liquid to flow.
In a gas:
The molecules are now moving around randomly at high speeds.
The molecules have broken the bonds between them: They are widely separated with no long-range forces binding them together.
As a result the molecules are able to move freely and so the gas can flow freely.
Because of the large spaces between the molecules (along with the absence of long-range forces) the gas can easily be compressed and is also able to expand.
The molecules in a gas move
The temperature of a gas is related to
The hotter the gas,
around randomly at high speeds.
the average speed of the molecules:
the faster the molecules move
pressure in gases
As the molecules move around, they collide with the surface of nearby walls.
Each collision applies a force across the surface area of the walls.
Pressure is
formula
the force per unit area:
Molecule Momentum in gases
When molecules collide against a wall, they bounce off, changing their momentum.
There are many such collisions every second, resulting in a large change in momentum each second.
This change in momentum each second results in a force being exerted against the wall:
The pressure exerted by the gas is equal to this force divided by the area of the wall.
Brownian Motion
When small particles (such as pollen or smoke particles) are suspended in a liquid or gas, the particles can be observed through a microscope moving around in a random, erratic fashion.
This movement is called Brownian Motion.
This motion is caused by molecules in the gas (or liquid) colliding at high speeds with the small particles.
These collisions give the particles a little nudge, causing them to change their speed and directions randomly, each time they are struck by a molecule.
This effect provides important evidence concerning the behaviour of molecules in gases.
Massive Particles Moved by Small Molecules
explain
The small particles observed in Brownian motion are significantly bigger than the molecules that cause the motion.
The molecules are able to affect the particles in this way because they are travelling at very high speeds (much higher than the particles) and so have a lot of momentum, which they transfer to the particles when they collide.
Evaporation is a
change in state of a liquid to a gas that can happen at any temperature from the surface of a liquid.
The molecules in a liquid have a range of different energies:…
Evaporation occurs when
When this happens energy is lost from the liquid:
Some have lots of energy, others have very little.
more energetic molecules near the surface of the liquid have enough energy to escape.
The average energy of the remaining molecules decreases.
This means that the temperature of the remaining liquid will also decrease.
Boyle’s Law
If a gas has an original pressure, P1, and temperature, V1, then its final pressure and temperature (P2 and V2) will be given by the relationship:
Note: The above equation only works if the temperature of the gas remains constant
