Phase Changes and Phase Diagrams

Phase Changes and Phase Diagrams

by Luis Bello

​Previous class.

​10.2 Properties of Liquids

Learning Objectives

• Distinguish between adhesive and cohesive forces

• Define viscosity, surface tension, and capillary rise

• Describe the roles of intermolecular attractive forces in each of these properties/phenomena

Multiple Choice

What is viscosity?

• A liquid's resistance to flow.

• a liquids flow.

• a liquid

• gas to solid.

Multiple Choice

Low viscosity is when particles are farther apart and the cohesive force is stronger.

• True

• False

• I don't know

Multiple Choice

Liquids with very high viscosity flow very _______________________.

• fast

• not at all

• slow

• whenever it wants

Multiple Choice

As temperature increases viscosity _______________.

• increases

• stays the same

• decreases

Multiple Choice

Which of the following is NOT a property of a liquid

• surface tension

• viscosity

• capillary action

• polar

Multiple Choice

Water droplets are mainly formed by what force?

• Viscosity

• Hydrogen Bonding

• Van der Waals forces

• Dipole-Dipole interactions

Multiple Choice

Capillary action is

• Caused by cohesive and adhesive forces

• Allows some liquids to 'flow' vertically up a thin tube

• Not observed in liquid mercury

• All of the above

Multiple Choice

Cohesive forces

• Are the attraction of molecules within a liquid

• Are the attraction of molecules to the container walls

• Are only present when the liquid is exposed to glue

• Are important for upward movement in capillary action

​Liquid to Gas Phase Transition

Vaporization of a sample of liquid is a phase transition from the liquid phase to the gas phase.

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Phase Transition: Liquid to Gas

Vaporization of a sample of liquid is a phase transition from the liquid phase to the gas phase. There are two types of vaporization: evaporation and boiling.

• Evaporation occurs at temperatures below the boiling point, and occurs on the liquid’s surface. For molecules of a liquid to evaporate, they must be located near the surface, be moving in the proper direction, and have sufficient kinetic energy to overcome intermolecular forces present in the liquid phase.

• Boiling, by contrast, is rapid vaporization that occurs at or above the boiling temperature and at or below the liquid’s surface.

​Dew Point: the atmospheric temperature (varying according to pressure and humidity) below which water droplets begin to condense and dew can form.

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​Supercritical Fluids

​A supercritical fluid is a substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist.

​Liquid to Solid Phase Transition

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Freezing is a phase transition in which a liquid turns into a solid when its temperature is lowered to its freezing point.

​Solid to Gas Phase Transition

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Sublimation is the phase transition from the solid to the gaseous phase, without passing through an intermediate liquid phase.

​​Heating Curve for Water

Water transitions from ice to liquid to water vapor as heat is added to it.

​Phase Diagrams

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Major Features of a Phase Diagram

Phase diagrams are useful because they allow us to understand in what state matter exists under certain conditions.