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TGB4:
Notes on effect of melting on sample size
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LINKS |
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What
happens to the size of a sample on melting?
The point about the very small expansion on melting is important
because students may expect there to be a large
increase in volume on melting.
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Most students will be familiar
with the idea that things expand when heated |
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Most students will
be aware that ice takes up more space than the same
mass of liquid water but may not necessarily realise
that water is a rather unusual substance. |
(In reality, metals typically increase volume by up
to 10% on melting, but bismuth and gallium contract slightly;
sodium chloride shows approximately 22% increase in volume,
but lithium fluoride shows an increase of over 30% in volume).
The students’ prior knowledge might lead them to expect
that the spacing between particles also increases considerably
as a solid melts, so it is important for students to understand
that the change of melting itself is due to changes in the
movement of the particles rather than significant changes
in the spacing or changes in the particles themselves.
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Science Enhancement Programme CD-ROM 2005 |
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user
guide |
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