4) States of matter Flashcards
Gas pressure
- gases in a container exert a pressure as the gas molecules are constantly colliding with the walls of the container
Changing gas volume
(decreasing it at constant temperature)
- causes molecules to be squashed together which results in more frequent collisions with the container wall
- pressure of the gas increases
- volume is therefore inversely proportional to the pressure
- graph of volume of gas plotted against 1/pressure gives a straight line
Changing gas temperature
(increasing it at constant volume)
- causes molecules to gain more kinetic energy
- the particles will therefore move faster and collide with the container walls more frequently
- pressure of gas increases
- temperature is therefore directly proportional to pressure
- graph of temperature of gas plotted against pressure gives a straight line
Kinetic theory of gases states that molecules in a gas are constantly moving and makes the following assumptions:
- the gas molecules are moving very fast and randomly
- the molecules have negligible volume
- no intermolecular forces
- no kinetic energy is lost when the gas molecules collide with each other (elastic collisions)
- temp of gas is related to average kinetic energy of the molecules
Ideal and real gases
Ideal- gases that follow the kinetic theory
Real gases- do not fit the kinetic theory of gases but may come very close to it
The volume than an ideal gas occupies depends on ?
Temperature
Pressure
When a gas is heated (at constant pressure) …
- the particles gain more kinetic energy and undergo more frequent collisions with the container wall
- to keep the pressure constant, the molecules must get further apart and therefore the volume increases
- volume is directly proportional to temperature (at constant pressure)
Volume and temperature
- volume is inversely proportional to pressure
- temperature is directly proportional to pressure
- volume is directly proportional to temperature
Limitations of the ideal gas law
At very high pressure and low temperature real gases do not obey the kinetic theory as under these conditions:
- molecules are close together
- there are id-id or pd-pd forces between the molecules and these forces pull the molecules away from the container wall
- volume of the molecules is not negligible
Real gases therefore do not obey the following kinetic theory assumptions at high temperatures and pressures, however ideal gases do because:
- there are no intermolecular forces of attraction between molecules
- volume of the gas molecules can be ignored
Ideal gas equation
pV=nRT
or
Mr= mRT/pV
Lattice structures of a crystalline solid
- most ionic, metallic and covalent compounds are crystalline lattices
- there molecules, atoms, ions are arranged in a regular repeating arrangement
4 types of structures
1) Giant ionic- sodium chloride and magnesium oxide
2) Simple molecular (covalent) - iodine, buckminsterfullerene C60 and ice
3) Giant molecular (covalent)- silicon IV oxide, graphite and diamond
4) Giant metallic- copper
Giant ionic
- high m.p and b.p
- only conduct electricity when molten or in a solution so that ions can move freely and conduct
- soluble in water and form ion-dipole bonds
- strong due to electrostatic forces (ionic crystals can be split apart)
- solid at room temp
- electrostatic attraction between ions
- ions
Giant metallic
- moderately high m.p and b.p
- conduct electricity when solid or liquid as there are mobile electrons
- insoluble, but some can react
- hard due to strong attractive forces between metal ions and delocalised electrons
- malleable
- solid at room temp
- positive ions in a sea of delocalised electrons