A. Major Points and Concepts
States of Matter
Solid-rigid, has a fixed volume and shape
Liquid-has a definite volume but takes the shape of its container
Gas-has no fixed volume or shape; it takes the shape and volume of its container
Phase Change
Evaporation
Boiling
Condensation
Freezing
Melting
Evaporation
change of phase from liquid to gas that occurs at the surface of a liquid
the temperature of any substance is related to the average kinetic energy of its particles
some particles have low kinetic energy and some have high kinetic energy
when there is enough kinetic energy in a particle, the particle can escape in to the atmosphere
when the molecule leaves, there is less energy in the system.
the lower kinetic energy=lower temperature
we have sweat gland in order to reduce our temperature
Some animal like pigs and dogs do not have sweat glands
They must find other method to cool down
Condensation
the changing of a gas to a liquid
kinetic energy-energy of attraction
when gas molecules near the surface of a liquid are attracted to the liquid, they strike the surface with increase kinetic energy and become part of the liquid
condensation is a warming process
steam burns are more painful than a burn from boiling water at the same temperature
the steam releases considerable energy when it condenses to a liquid and wets the skin
this release of energy is used by steam heating systems
Questions
What would happen when there is more evaporation than condensation? cooling
What would happen when there is equal amount of evaporation and condensation? no change
What would happen when there is more condensation than evaporation? increase in temperature
Fog and Clouds
Warm air rises and expands.
When the air expands, it chills and the water molecules will slow down and stick together.
Clouds and fogs form when lots of molecules stick together
Boiling
Change liquid to gas
like evaporation
major difference
evaporation only occurs at the surface
boiling can occur in any liquid
Bubbles
in liquid can form only when the pressure of the vapor with in the bubbles is great enough to resist the pressure of the surrounding liquid
Boiling point
a temperature at which a liquid boils
pressure affect the boiling point
increase pressure boiling point increases
decrease pressure boiling point decreases
boiling point is at standard pressure
Freezing
when kinetic energy is low and the energy of attraction is greater, a liquid will freeze
different liquids have different freezing points
Melting
if the kinetic energy is high enough to equal to energy of attraction then the solid becomes a liquid
Energy and Phase change
heat of fusion
the amount of energy/mol needed to convert between solid and liquid
H2O-6kJ/mol
heat of vaporization
the amount of energy/mol needed to convert between a liquid and a gas
H2O-41kJ/mol
Forces
Intramolecular Forces
Forces in a molecule
covalent
ionic
Intermolecular forces
forces between molecules
Dipole-Dipole
hydrogen bonding
London dispersion forces
Vapor pressure
in a sealed container, a given amount of liquid in a container will decrease slightly.
eventually, the volume will become constant
the rate of evaporation and condensation will equal
Sublimation
the process of changing from a solid to a gas without passing through an intermediate liquid phase
Deposition
the process of changing from a gas to a solid without passing through an intermediate liquid phase
Ionic Solids
are stables substances with high melting points that are held together by strong forces existing between oppositely charge ions
Molecular Solids
tends to melt at relatively low temperature because the intermolecular forces that exist among the molecules are relatively weak
If the molecules has a dipole moment, then the dipole-dipole forces hold the solids together
If the molecules is nonpolar, then london dispersion forces holds the solids together
Alloy
a substance that contains a mixture of elements and has metallic properties
Common types of alloys
Substitutional alloy
ex: brass
Interstitial alloy
ex: Steel
Solid-rigid, has a fixed volume and shape
Liquid-has a definite volume but takes the shape of its container
Gas-has no fixed volume or shape; it takes the shape and volume of its container
Phase Change
Evaporation
Boiling
Condensation
Freezing
Melting
Evaporation
change of phase from liquid to gas that occurs at the surface of a liquid
the temperature of any substance is related to the average kinetic energy of its particles
some particles have low kinetic energy and some have high kinetic energy
when there is enough kinetic energy in a particle, the particle can escape in to the atmosphere
when the molecule leaves, there is less energy in the system.
the lower kinetic energy=lower temperature
we have sweat gland in order to reduce our temperature
Some animal like pigs and dogs do not have sweat glands
They must find other method to cool down
Condensation
the changing of a gas to a liquid
kinetic energy-energy of attraction
when gas molecules near the surface of a liquid are attracted to the liquid, they strike the surface with increase kinetic energy and become part of the liquid
condensation is a warming process
steam burns are more painful than a burn from boiling water at the same temperature
the steam releases considerable energy when it condenses to a liquid and wets the skin
this release of energy is used by steam heating systems
Questions
What would happen when there is more evaporation than condensation? cooling
What would happen when there is equal amount of evaporation and condensation? no change
What would happen when there is more condensation than evaporation? increase in temperature
Fog and Clouds
Warm air rises and expands.
When the air expands, it chills and the water molecules will slow down and stick together.
Clouds and fogs form when lots of molecules stick together
Boiling
Change liquid to gas
like evaporation
major difference
evaporation only occurs at the surface
boiling can occur in any liquid
Bubbles
in liquid can form only when the pressure of the vapor with in the bubbles is great enough to resist the pressure of the surrounding liquid
Boiling point
a temperature at which a liquid boils
pressure affect the boiling point
increase pressure boiling point increases
decrease pressure boiling point decreases
boiling point is at standard pressure
Freezing
when kinetic energy is low and the energy of attraction is greater, a liquid will freeze
different liquids have different freezing points
Melting
if the kinetic energy is high enough to equal to energy of attraction then the solid becomes a liquid
Energy and Phase change
heat of fusion
the amount of energy/mol needed to convert between solid and liquid
H2O-6kJ/mol
heat of vaporization
the amount of energy/mol needed to convert between a liquid and a gas
H2O-41kJ/mol
Forces
Intramolecular Forces
Forces in a molecule
covalent
ionic
Intermolecular forces
forces between molecules
Dipole-Dipole
hydrogen bonding
London dispersion forces
Vapor pressure
in a sealed container, a given amount of liquid in a container will decrease slightly.
eventually, the volume will become constant
the rate of evaporation and condensation will equal
Sublimation
the process of changing from a solid to a gas without passing through an intermediate liquid phase
Deposition
the process of changing from a gas to a solid without passing through an intermediate liquid phase
Ionic Solids
are stables substances with high melting points that are held together by strong forces existing between oppositely charge ions
Molecular Solids
tends to melt at relatively low temperature because the intermolecular forces that exist among the molecules are relatively weak
If the molecules has a dipole moment, then the dipole-dipole forces hold the solids together
If the molecules is nonpolar, then london dispersion forces holds the solids together
Alloy
a substance that contains a mixture of elements and has metallic properties
Common types of alloys
Substitutional alloy
ex: brass
Interstitial alloy
ex: Steel