Chapter 14: Change of Phases States of Matter: - Solid: rigid; has a fixed shape and volume - 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
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
Questions? - What would happen when there is more evaporation than condensation? - Cooling
- What would happen when there is equal amount of evaporation & 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 (solid to liquid) - The amount of energy/mol needed to convert between solid and liquid. - H2O~ 6 kJ/mol - Heat of Vaporization (liquid to gas) - The amount of energy/mol needed to convert between a liquid and a gas. - H2O~ 41 kJ/mol
Forces: - Intramolecular Forces - Forces in a molecule - Covalent - Ionic - Intermolecular Forces - Forces between molecules - Dipole-dipole - hydrogen bonding - London dispersion forces
Hydrogen bonding:
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.
Crystalline Solids:
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 - example Brass - Interstitial alloy - example Steel