The Science of S'mores Chemistry Article for Students | Scholastic Science World Magazine (2024)

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The first step to making a s’more is simple. Toast a marshmallow over an open flame (see On Fire). “Combustion is a chemical reaction,” says Sally Mitchell. She’s a chemistry teacher in Syracuse, New York, and an expert for the American Chemical Society. New substances form during a chemical reaction.

A marshmallow is mostly sugar. It’s whipped with air to make it fluffy. The treat also contains a stretchy molecule called gelatin. This gives a marshmallow its form. Gelatin is made up of proteins. These large molecules are important to all living things. A campfire’s heat causes the sugar and proteins in a marshmallow to chemically react. They form new substances. One of these is the brown crust on the outside of a toasted marshmallow.

Once toasted, the marshmallow and a square of chocolate are sandwiched between two graham crackers. The hot marshmallow melts the chocolate. “It changes phases from a solid to a liquid,” says Mitchell. “This is a physical change because the chocolate’s components remain the same.”

The sticky chocolate and marshmallow hold a s’more together. The graham crackers play an important role too—they keep your fingers from getting too messy as you munch the sweet treat.

The toasted marshmallow and a square of chocolate are placed between two graham crackers. The hot marshmallow melts the chocolate. “It changes phases from a solid to a liquid,” says Mitchell. “This is a physical change because the chocolate’s components remain the same.”

The sticky chocolate and marshmallow hold a s’more together. The graham crackers play an important role too. They keep your fingers from getting too messy as you munch the sweet treat.

1. A graham cracker’s perforations make it easy to break in half to become the top and bottom of a s’more.
2. Toasting a marshmallow over a flame causes a chemical reaction between the sugar and gelatin in the marshmallow, turning its outside brown and crispy. A marshmallow’s melting point—the temperature at which a solid becomes a liquid—is about 45°C (113°F). So as its outside crisps, its insides become gooey.
3. A chocolate bar’s indentations allow it to be broken into pieces that fit perfectly on a graham cracker half. A hot marshmallow melts the chocolate, which has a melting point of about 33°C (91°F). That physical change secures the snack together.

1. The dotted lines on a graham cracker make it easy to break in half. The pieces become the top and bottom of a s’more.
2. When you toast a marshmallow over a flame, a chemical reaction happens between the sugar and gelatin in the marshmallow. The reaction turns its outside brown and crispy. A marshmallow’s melting point is about 45°C (113°F). That’s the temperature at which a solid becomes a liquid. So as its outside crisps, its insides become gooey.
3. A chocolate bar easily breaks into pieces along its grooves. The pieces fit perfectly on a graham cracker half. Chocolate’s melting point is about 33°C (91°F). A hot marshmallow melts the chocolate. That physical change makes the snack stick together.