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How does clicking a reusable hand warmer make it heat up?

Click a metal disk inside a reusable hand warmer and crystals spread through the liquid as the pack heats up. The click starts a change in a sodium-acetate mixture; it does not supply all that warmth. Explore where the stored energy came from and what resetting the pack requires.

3–7 min

Questions you could explore

  • How is a trigger different from the energy source for the change it starts?
  • How does crystallization release stored energy in a reusable hand warmer?

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Chemistry and materials

From dissolved minerals to kettle limescale

Rainwater starts out soft, but as it percolates through limestone and chalk, it dissolves minerals that travel invisibly to your kitchen tap. That dissolved calcium and magnesium is what makes water 'hard', and when a kettle heats the water, the chemical balance shifts and leaves solid calcium carbonate behind as crusty limescale.

3–5 min

From dissolved minerals to kettle limescale

Chemistry and materials3–5 minRainwater starts out soft, but as it percolates through limestone and chalk, it dissolves minerals that travel invisibly to your kitchen tap. That dissolved calcium and magnesium is what makes water 'hard', and when a kettle heats the water, the chemical balance shifts and leaves solid calcium carbonate behind as crusty limescale.

Chemistry and materials

Why does ice take up more room than water?

An ice cube floats in the water it came from, and freezing water can push against its container. Ordinary ice arranges water molecules differently from the liquid, connecting a microscopic pattern with a familiar change in volume.

3–5 min

Why does ice take up more room than water?

Chemistry and materials3–5 minAn ice cube floats in the water it came from, and freezing water can push against its container. Ordinary ice arranges water molecules differently from the liquid, connecting a microscopic pattern with a familiar change in volume.

Chemistry and materials

Identifying elements through patterns of light

A glowing gas can produce a pattern of spectral lines characteristic of its elements. Comparing several lines gives more evidence than spotting one color or line alone, while temperature, motion, and other conditions also affect the spectrum.

5–7 min

Identifying elements through patterns of light

Chemistry and materials5–7 minA glowing gas can produce a pattern of spectral lines characteristic of its elements. Comparing several lines gives more evidence than spotting one color or line alone, while temperature, motion, and other conditions also affect the spectrum.

How does clicking a reusable hand warmer make it heat up? | Speech Topic | speaking.app