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•The Nature of Liquids
Liquids
• The ability of gases and liquids to flow allows then to conform to the shape of their containers.
• Liquids are much more dense then gases.
More on liquids….
»Increasing the pressure on a liquid has hardly any effect on its volume. (The same is true of solids).
»For that reason, liquids and solids are known as condensed states of matter.
Key Concept!!!
• The interplay between the disruptive motions of particles in a liquid and the attractions among the particles determines the physical properties of liquids.
Evaporation & Vaporization• The conversion of a liquid to a gas or
vapor is called vaporization.
• When such a conversion occurs at the surface of a liquid that is not boiling, the process is called evaporation.
Key Concept • During evaporation, only those
surface molecules with a certain minimum kinetic energy can escape from the surface of the liquid.
More on Evaporation….
• Liquid evaporates faster when heated. This is because heating a liquid increases the average kinetic energy of its particles.
• As evaporation occurs, the particles with the highest kinetic energy escape first.
• Evaporation is a cooling process!!
Vapor Pressure
Vapor (Gas)Liquid
evaporation
Condensation
• An increase in temperature of a contained liquid increases the vapor pressure.
Boiling Pointvapor pressure = external pressure
• When a liquid is heated to a temperature at which particles throughout the liquid have enough kinetic energy to vaporize, the liquid begins to boil.
• Because atmospheric pressure is lower at higher altitudes, boiling points decrease at higher altitudes.
• Although vapor has the same kinetic energy as the liquid, its potential (or stored energy) is much higher.
»Thus a burn from steam is more severe than one from an equal mass of boiling water at the same temperature.
The Nature of Solids
• The general properties of solids reflect the orderly arrangement of their particles and the fixed locations of their particles.
Melting Point
Solid Liquid
Melting
Freezing
Crystal Structure
• The type of bonding that exists between particles in crystals determines their melting points.
» Not all solids melt however. » Wood and cane sugar for example,
decompose when heated.
• Allotropes are two or more different molecular forms of the same element in the same physical state.
Graphite
DiamondFullerene
Allotropes of Carbon
• Amorphous Solids lack an ordered internal structure.
»Rubber, plastic and asphalt are examples
Changes of State
• Sublimation is the change of a substance to a vapor without passing through the liquid state.
Phase Diagrams
• A phase diagram gives the conditions of temperature and pressure at which a substance exists as a solid, liquid and gas (vapor).
Phase Diagram Cont…
• The Triple Point describes the only set of conditions at which all three phases can exist in equilibrium with one another.
• A decrease in pressure lowers the boiling point and raises the melting point
• An increase in pressure will raise the boiling point and lower the melting point.