Chapter 14
- Solids- they have a define shape and volume
- Liquids- define volume but assumes the shape of the container
- Gases- No define shape or volume - - Liquid and gas are considered fluids
- - Gases flow like liquids and are fluids.
- - The difference between a gas and a liquid is the distance between the molecules.
Phase Changes
- 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 particles 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 gland.
- 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
Practice
- 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 expand.
- When the air expand it is chills and the water molecules will slow down and stick together.
- Clouds and fogs are form when lots of molecules stick together.
Boiling
- Changes liquid to gas.
- Like evaporation
- Major difference
- Evaporation only occurs at the surface
- Boiling can occur any in the liquid.
- Boiling point
- A temperature at which a liquid boils.
- Pressure affect the boiling point
- increase pressure boiling points increase
- Decrease pressure boiling point decreases.
- 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~ 6 kJ/mol
- Heat of Vaporization
- The amount of energy/mol needed to convert between a liquid and a gas.
- H2O~ 41 kJ/mol
- 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 be come 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
- Two Types of Alloys
Substitutional alloy
example Brass
Interstitial alloy
example Steel
Links!
Resources
http://www.school-for-champions.com/science/matter_states_changing.htm#.Uzoyfv2QxuY
http://www.kentchemistry.com/links/Matter/PhaseChanges.htm
Video
www.youtube.com/watch?v=lTKl0Gpn5oQ
http://www.khanacademy.org/science/chemistry/states-of-matter/v/specific-heat--heat-of-fusion-and-vaporization
Worksheet
http://s3.amazonaws.com/scschoolfiles/237/phase_changes_worksheet.pdf
http://www.mayfield.k12.oh.us/userfiles/1250/Classes/10325/phase%20change%20worksheet%20and%20key-0.pdf
- Evaporation only occurs at the surface
- Boiling can occur any in the liquid.
- The amount of energy/mol needed to convert between solid and liquid.
- H2O~ 6 kJ/mol
- The amount of energy/mol needed to convert between a liquid and a gas.
- H2O~ 41 kJ/mol
- Forces in a molecule
- Covalent
- Ionic
- Forces between molecules
- Dipole-dipole
- hydrogen bonding
- London dispersion forces