Thermal Energy & States of Matter
Aligned to MS-PS1-4 — Next Generation Science Standards.
What this lesson teaches
Adding thermal energy makes particles move faster and spread apart, which can raise the temperature or change the state. Removing thermal energy slows the particles and can cause condensing or freezing.
Worked examples
Example 1
When you heat ice, the water molecules vibrate faster until they break free and slide past each other as liquid water. Keep heating and they move fast enough to escape into the air as water vapor.
Example 2
While ice is melting, its temperature stays at 0 °C even though you keep adding heat — that energy is going into breaking the bonds, not raising the temperature.
Example 3
A state change is physical, not chemical. The water molecules in steam are exactly the same molecules that were in the ice.
Practice questions
- Observe a beaker of melting ice and describe what happens to the spacing between particles.
- Draw a particle model of the same substance as a solid, a liquid, and a gas.
- Explain why the temperature stays constant while ice is melting even though heat is still being added.
Watch the lesson
Every lesson comes with a video taught in English and Spanish — the same video the QR code in the printed workbook opens.
▶ Watch this lessonEn español
Energía Térmica y Estados de la Materia
Agregar energía térmica hace que las partículas se muevan más rápido y se separen, lo que puede subir la temperatura o cambiar el estado. Quitar energía térmica frena las partículas y puede provocar condensación o congelación.
Ejemplo 1: Cuando calientas hielo, las moléculas de agua vibran más rápido hasta que se sueltan y se deslizan unas junto a otras como agua líquida. Si sigues calentando, se mueven tan rápido que escapan al aire como vapor de agua.
Ejemplo 2: Mientras el hielo se derrite, su temperatura se queda en 0 °C aunque sigas agregando calor — esa energía va a romper los enlaces, no a subir la temperatura.
Ejemplo 3: Un cambio de estado es físico, no químico. Las moléculas de agua del vapor son exactamente las mismas que estaban en el hielo.
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