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Metallic Bonds and Heat of Vaporization
Name: Carla
Status: student
Grade: 9-12
Location: IL
Country: USA
Date: Summer 2009
Question:
In metallic bonds, what is heat vaporization?
Replies:
Hi Carla, perhaps you mean the heat of vaporization (added "of")? Heat
of vaporization is the amount of energy required for a substance to
undergo a phase change and turn into gas (vaporization). This assumes
no temperature change, so typically this quantity is measured at the
boiling point of liquids. For example, if you have water that is at
its boiling temperature, around 100C at sea level, it takes additional
energy for the water to turn to gas - you have to keep heating it to
keep it boiling even if you are already at 100C. This extra energy is
known as the heat of vaporization. You might notice when you are
boiling water (and this is an experiment you can do yourself -- but
use proper safety technique!), that when you start heating cool water,
its temperature rises steadily. However, once it reaches boiling
point, the temperature stops rising, even though you are still adding
heat. The reason for this is because the heat absorbed by the water is
now being used to vaporize (boil) the water instead of raising its
temperature. If you search on the Internet for "heat of vaporization",
you can read a lot more about this topic. In the context of metal,
metals also have their own respective heats of vaporization, so the
principle is the same, although molten metals typically require much,
much higher temperatures than water.
If I am not understanding your question properly, write back and I can
try again.
Hope this helps,
Burr Zimmerman
Even metals evaporate, although usually at high temperature. However, mercury
"boils" at about 350 C. Its heat of vaporization is about 59 kJ/mol. There is
nothing "magical" I can think of that is unique to metals compared to other
substances, except that metals tend to have high boiling points.
As with other substances one has to be aware of what species are present in the
vapor vs. liquid phase.
Vince Calder
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Update: June 2012
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