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BeCsLi 2010IV. Phase Change-Occurs as a result of addition or removal of heat; also involves breaking of IMF

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BeCsLi 2010Phase Changes

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BeCsLi 2010Heating Curve

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BeCsLi 2010Phase Diagram- a graphical way to summarize the conditions under which equilibrium exist between the different states of matter. It allows us to predict the phase of a substance that is stable at any given temperature and pressure

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• Triple Point: where all three phases are in equilibrium

• Critical Point: point where critical Temp. and Pressure is achieved

• Critical Temperature: highest temperature at which a distinct liquid phase can form

• Critical Pressure: pressure required to bring about liquefaction at critical temperature

• Boiling point: temp. at which the vapor pressure of a liquid equals the atmospheric pressure. IMF strength, B. Pt. (normal B.Pt.: B. Pt. at 1 atm)

• Melting point: temp. at which liquid and solid phase coexists in equilibrium. Under same pressure, solids with IMF strength have M. Pt.

TERMS

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BeCsLi 2010V. Properties of liquid- Liquids are almost incompressible, assume the shape but not the volume of container:- Liquids molecules are held closer together than gas molecules, but not so rigidly that the molecules cannot slide past each other.

1.Viscosity – liquid’s resistance to flow due to IMF which impedes movement

- increase in surface area of the molecule results to increase in viscosity. Explain why.- increase in temperature results to decrease in viscosity. Why?

What is the relationship of Viscosity and IMF?

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BeCsLi 2010

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BeCsLi 20102. Surface Tension

- amount of energy required to increase the surface area of a liquid

- measure of the “cohesive force that must be overcome”

Liquid surface tends to have the smallest possible area

What is the relationship of Surface Tension and IMF?

Compare water, mercury and ethanol in terms of S.T.

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BeCsLi 2010

3. Capillarity/ Capillary Action– rising of a liquid through a narrow space against the pull of gravity

Cohesive Force – binds molecules to each other (IMF)Adhesive Force – binds molecules to a surface

Meniscus - the shape of the liquid surface. adhesive forces > cohesive forces the liquid surface is attracted to its container more than

the bulk molecules. Therefore, the meniscus is U-shaped (e.g. water in glass).

cohesive forces > adhesive forcesthe meniscus is curved downwards