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States of Matter and Intermolecular Forces
3 Phases of Matter
SolidLiquidGas
How do particles move in a solid?
Solids
Have a definite shape/structure
Very little particle movement—fixed position
Liquids
Limited structure to particles
Movement is less restricted, particles can move around and collide with each other
Conform to a container’s shape
Gases
No structure
Movement is not restricted
Particles are always in motion
Expansion occurs
Phase Changes
Physical change of a chemical compound
Change of state
Types: Melting
Freezing
Vaporization
Condensation
Sublimation
Deposition
Evaporation/Vaporization
Liquid---gas, endothermic
Liquid molecules gain enough energy to enter the gaseous state via breaking intermolecular forces.
Enthalpy of vaporization— Amount of heat necessary to evaporate a liquid at constant
temperature
kJ/mole
Table 11.1 (p. 435)
Condensation
Gas-----liquid
Exothermic process
Example 1
At 25°C, how much heat is required to evaporate 175 g of methanol?
Example 2:
Which liquid in Table 11.1 (p. 435) requires the lowest amount of heat for vaporization?
Vaporization/Condensation
Processes exist at the same time
Dynamic equilibrium is established Rate of vaporization = rate of condensation
No net change in molecular movement
Many factors determine how long it will take for equilibrium to be established
Vapor Pressure
Characteristic of liquid
Partial pressure of vapor when it exists with a liquid in dynamic equilibrium under constant temperature
Dependent on liquid type and temperature at equilibrium
INCREASE vapor pressure of liquid, INCREASE temperature
Vapor Pressure Curve
Figure 11.4 p. 439
Volatile vs. Nonvolatile Liquids
1) Volatile Liquids WEAK intermolecular forces
High vapor pressure
Ex. Gasoline, alcohols, “Whoosh Bottle”
2) Nonvolatile Liquids STRONG intermolecular forces
Low vapor pressure
Whoosh Bottle Demo Video
http://www.youtube.com/watch?v=-BtFHg-lm_M
Boiling Point
Liquid characteristic
Vaporization present throughout the liquid
Point where vapor pressure = atmospheric pressure
Aids in liquid identification
Decrease atmospheric pressure with increased altitude, lowers boiling point
Boiling Point (cont.)
Critical temperature/pressure (TC , PC)
Highest temperature with liquid and vapor present as physically different states in equilibrium
Point where increased pressure only will result in condensation
Critical Point Actual physical condition where critical temperature and pressure
achieved
Melting/Melting Point
Melting/freezing point Temperature when solid “melts”
Temperature when liquid becomes solid
For water = _________
Enthalpy (heat) of fusion– Δhfusion
Amount of heat needed to convert a certain amount of a solid to a liquid
Melting—endothermic
Freezing—exothermic (- value)
Cooling/Heating Curves
Figure 11.7 p. 444
Cooling/Heating Curves
Sublimation
Solid Gas
Some solid compounds are volatile enough to have a vapor pressure and convert to gas Ex. Mothballs, dry ice
Rate of sublimation = rate of deposition
Sublimation curve
Sublimation pressure— Pressure of a vapor existing in equilibrium with a solid
Enthalpy (heat) of sublimation
= ΔHfusion + ΔHvapn