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 The raining animals The raining animals Evaporation is the process that changes a liquid into a gas. Evaporation is a surface phenomenon and it is the process that helps in maintaining the water content on Earth surface. Evaporation brings the water back into the air to the clouds over time. The water in the clouds precipitates as rains. Raining animals is a rare meteorological phenomenon in which flightless animals "rain" from the sky. There have been reports of raining toads and fish in many countries throughout history. Do these animals go up during the process of evaporation? No. Scientists believed that tornadic waterspouts are the cause for this phenomenon since waterspouts are capable of capturing objects and animals and lifting them into the air.

Learning Objectives

After completing the topic, the student will be able to:

  • Recognize that liquids have intermediate properties of solids and gases.
  • Define surface tension and describe the capillarity phenomenon.
  • Understand the importance of surface tension on behavior of liquids.
  • Understand the importance of viscous properties of liquids.
  • Understand the evaporation process and list the factors affecting evaporation.
  • Define vapor pressure and discuss the factors effecting vapor pressure.
  • Relate boiling point and vapor pressure and explain the effects of intermolecular forces on boiling point.
  • Describe the heating and cooling curves and estimate the heat of vaporization.
Liquid Phase Liquid ‐ an intermediate phase Liquid is an intermediate phase between solid and gas. But it neither possesses the characteristics of solid nor gas. It has its own properties. Intermolecular forces are mainly responsible for the condensed state of liquids.
Liquid phase

Liquid is a form of matter between gas and a solid that has a definite volume, but no definite shape.

Liquids are made up of very small particles (atoms, molecules and or ions). Particles that make up the liquid are close together with no regular arrangement. These particles vibrate, move about, and slide past each other.

The particles in a liquid have more kinetic energy than the particles in the corresponding solid. As a result particles in liquid move faster in terms of vibration, rotation and translation. As they are moving faster, the particles in the liquid occupy more space. As a result of this, they have comparable values of densities and are less denser than a solid.

 Beaded droplets on waxy surfaces Beaded droplets on waxy surfaces The adhesive (dipole & induced dipole) forces between water and a non−polar surface are much weaker than the cohesive (H−bond) forces within water. As a result, water pulls away from a non−polar surface and forms beaded droplets. You might have experienced this effect when water beads upon a leaf or a freshly waxed car after a rainfall.
Intermolecular forces of liquids

In the three regular stages of matter, the liquid is less understood at molecular level. Because of randomness of particles in a gas, any region in the gas is virtually identical to each other. The orderliness of the particles in the solid at different regions, make the regions in it identical to each other. Liquid, however is a combination of the attributes that change continuously. A region that is ordered at this instant will be random in the next instant and vice versa. Despite this complexity, the properties of liquids are well understood.

Intermolecular forces give rise to a number of structural features and properties of liquids. Many properties of liquids, including their boiling points, reflect the strengths of the intermolecular forces. A liquid boils when bubbles of its vapour form within the liquid. The molecules of a liquid must overcome their attractive forces in order to separate and form a vapour. The stronger the attractive forces, the higher will be the temperature at which the liquid boils (Similarly, the melting points of solids increase with an increase in the strengths of the intermolecular forces).

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