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S'mores are sweet treats made from graham crackers, marshmallows, and chocolate.
What Burns? What Melts?
Imagine this: You're camping with your family.
It's a beautiful night, just perfect for sitting
around the campfire and making s'mores
under the stars. You layer a graham cracker,
a piece of chocolate, a marshmallow you've
toasted over the fire, and another graham
cracker-a sweet, sticky treat! You might
even leave your whole s'more sitting near
the fire to help melt the chocolate. In that
moment, the campfire is transferring energy
to the wood in the fire and to the chocolate.
but they're responding in very different ways.
The wood is burning, while the chocolate in
the s'more is melting. What's the deal?
Melting is a phase change from the solid phase
to the liquid phase. The molecules in a solid
chocolate bar are packed tightly together and
can only move in place. When energy is added
to the solid chocolate-like thermal energy
from a fire-the molecules gain energy and
begin to move around more. When they have
enough energy and freedom of movement
to flow around each other, the chocolate
becomes a liquid. It's important to remember
that melting doesn't change substances
into other substances. The molecules that
make up your chocolate bar haven't changed:
they're just moving around more. It's even
possible to make liquid chocolate back into
solid chocolate by removing energy-also
known as letting the chocolate cool.
The wood in your campfire is also receiving
energy from the fire, but it definitely isn't
melting into a liquid. Instead, it's burning.