Transcript Evaporation

Evaporation
F. 3A
Winnie Chan (6)
Lydia Chan (7)
Vikki Chan (8)
Stephanie Cheung (9)
Vivian Chiu (10)
What is evaporation?
• The water changes into water vapour in a
process called evaporation.
• Evaporation is the change of state from liquid
to gas below the boiling point. Boiling only
takes place at the boiling point, but
evaporation can take place in any
temperatures below the boiling point. In
addition, evaporation only takes place on the
surface of a liquid, where as boiling takes
place everywhere within the liquid.
The conversion of water from a liquid into a gas
•
Water is transferred
from the surface to
the atmosphere
through evaporation,
the process by which
water changes from a
liquid to a gas.
• Approximately 80% of all evaporation is from the
oceans, with the remaining 20% coming from
inland water and vegetation. Winds transport
the evaporated water around the globe,
influencing the humidity of the air throughout the
world.
• Most evaporated water exists as a gas outside of
clouds and evaporation is more intense in the
presence of warmer temperatures. This is shown
in the image above, where the strongest
evaporation was occurring over the oceans and
near the equator
Microscopic interpretation of evaporation
• Inside a liquid, the distribution of
kinetic energy of the particles is
random and some has higher and
some lower kinetic energies.
• The energetic particles have
enough energy to overcome the
attractive forces between them
and leave the liquid through the
liquid surface.
• The particles that leave the liquid
are the high-energy particles,
• The average kinetic energy of the
liquid particles decreases the
temperature of the liquid will
decreases.
• The liquid cools down during
evaporation.
• The evaporated vapour takes
away latent heat and cools down
the liquid.
Cooling effect of evaporation
• Sweating helps to maintain our body
temperature normal through evaporation.
Sweat is mainly water and when it
evaporates, it takes away latent heat of
vaporization from your body. When you
are exercising vigorously, your body
needs to lose more heat to maintain the
normal body temperature, so it produces
extra sweat. Dogs have no sweat gland,
they cool themselves by panting.
Rate of evaporation
•
The wind carries the water vapour away and
increases the rate of evaporation of sweat from your
body. In fact, there are many ways to increase the
rate of evaporation of a liquid:
1.
Increase the temperature of the liquid. One example
is that a puddle of water will dry up faster under the
sun than in the shades.
Increase the surface area of the liquid exposed. For
example, spilled water evaporates faster than when it
is in a glass.
Increase the movement of air near the surface of the
liquid. For example, clothes dry faster on a windy day.
Decrease the amount of vapour in the surrounding air.
For example, clothes dry faster on days with low
humidity than on days with high humidity.
2.
3.
4.
Resources
• http://ww2010.atmos.uiuc.edu/(Gh)/guide
s/mtr/hyd/evap.rxml
• http://www.phy.cuhk.edu.hk/contextual/h
eat/cha/evapo01_e.html
Thank You!!! XP