Mission 1: How can a glow stick glow without getting hot?

What's inside a glow stick

• A glow stick holds two solutions, kept apart.
• One is hydrogen peroxide, sealed in a thin glass tube.
• Around it, in the plastic tube, is a second solution: an oxalate ester and a dye.
• Bend the stick: the glass snaps and the two solutions mix.

No mixing, no reaction

• Particles can only react when they collide.
• Before you bend the stick, the two solutions can't meet: no reaction, no glow.
• Once they mix, their particles collide and react, and the glow starts.

Where the light comes from

• The chemicals store energy. The reaction releases some of it.
• Some is passed to the dye molecules, which give it out as light. The rest warms the surroundings very slightly.
• Light made directly by a chemical reaction is called chemiluminescence.
• The dye sets the colour: different dyes give different colours.

Hot light and cold light

• A filament bulb glows because its filament is extremely hot.
• A glow stick's light doesn't come from heat. It comes straight from the reaction.
• The energy comes out slowly, over hours. The heat escapes as fast as it is made, so the stick barely warms up.

Mission 2: Why does a glow stick last longer in the freezer?

Collision theory

• Particles can only react when they collide.
• Not every collision works. Particles must collide with at least a minimum amount of energy: the activation energy.
• The rate of reaction is how fast reactants are used up, or products are made.

What temperature does

• Heating makes particles move faster.
• They collide more often, and more collisions have at least the activation energy.
• More successful collisions each second: the rate increases.
• Cooling does the opposite: the rate decreases.

Brightness shows the rate

• The more particles react each second, the more light the stick gives out each second.
• Faster reaction: brighter, but the chemicals are used up sooner, so it fades sooner.

The freezer trick

• In a freezer, the particles still move, but more slowly.
• Fewer collisions, and fewer with enough energy: the reaction slows right down.
• The stick is dimmer, but uses its chemicals slowly, so it lasts longer.
• Take it out and it brightens as it warms. The cold slowed the reaction; it didn't stop it.

Same light, different speed

• The amount of chemical in the stick sets roughly how much light it can give out in total.
• Temperature changes how fast that light comes out.
• Warm: bright, but short. Cold: dim, but long.

Mission 3: What's the fairest way to test the freezer trick?

Three kinds of variable

• Independent variable: the one you change. Here, temperature.
• Dependent variable: the one you measure. Here, how fast the glow fades.
• Control variables: everything you keep the same, so only temperature can cause a difference.

Plan it, then try it at home

• Three water baths: iced, room temperature, warm (warm enough to hold your hand in comfortably; an adult checks it). Check each with a thermometer and top it up to keep it steady.
• Glow sticks of the same brand, size and colour, bent at the same moment.
• At set times, take each stick out for the same few seconds and read it with the same phone and app, propped at the same marked distance, in a dark room. Take the first reading straight after bending.
• Record the time for each stick's reading to fall to half its first reading.

Measuring well

• "When I can't see it any more" depends on your eyes and the room. It's subjective.
• A light-meter app gives a number. Phone readings are estimates, but that's fine here: each stick is only compared with its own first reading.
• Repeat each temperature. Repeats show whether results are repeatable and help you spot anomalous ones.
• Leave out any result that is clearly anomalous, then calculate a mean of the rest.

Stay safe at home

• Try it with an adult. Never cut or break open a glow stick: inside are sharp glass and chemicals that irritate skin and eyes.
• Warm bath: comfortable to hold your hand in, never hot. Never use boiling water or a microwave.
• On skin: wash with soap and water. In eyes: rinse with water for at least 15 minutes, and tell an adult.

🧪 Try it at home, with an adult. Keep every stick sealed.

Nature's glow sticks

• Fireflies make their light with a chemical reaction too.
• An enzyme called luciferase speeds that reaction up and isn't used up: it's a catalyst.
• Many deep-sea anglerfish have a glowing lure, lit by bacteria that live inside it.

The big ideas

• Bending mixes two solutions, so their particles can collide and react.
• The reaction passes some energy to a dye, which gives it out as light: chemiluminescence.
• Warmer particles collide more often and with more energy: a faster reaction.
• Warm: bright but short. Cold: dim but long. Roughly the same light in total.
• A fair test changes only the independent variable. An instrument replaces a judgement with a number.