A 100-gram sample of tin undergoes a
phase change from solid to liquid. Is the mass of liquid tin equal to, less
than, or greater than the mass of tin in the original sample?
So what we have is 100 grams of solid tin
where the atoms of tin are all locked in place. This tin has undergone a phase change
from solid to liquid, so it’s melted. And the atoms are now free to move around
one another. What we need to answer is whether the
mass of the liquid tin has gained mass, lost mass, or kept the same mass as the original
solid tin. The law of conservation of mass says the
mass of a closed system cannot change. A phase change is an example of a
physical process where there’s no chemical change. For a physical process like this, the
mass before equals the mass after.
In this scenario, our system consists of
all the tin atoms. After melting, the system still contains
all the original atoms of tin. So the mass of the system is the
same. So the mass of liquid tin is 100
grams. The mass of liquid tin is, therefore,
equal to the mass of tin in the original sample.