Energy in Chemical Reactions
Aligned to HS-PS3 — Next Generation Science Standards.
What this lesson teaches
Reactions absorb or release energy. Exothermic reactions release heat; endothermic reactions absorb it. Total energy is conserved.
Worked example
Burning wood is exothermic — it releases heat and light. A cold pack is endothermic — it absorbs heat, feeling cold.
Practice questions
- Classify burning fuel as exo- or endothermic.
- Where does the energy in an exothermic reaction go?
- Why is energy conserved in a reaction?
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 en las Reacciones Químicas
Las reacciones absorben o liberan energía. Las reacciones exotérmicas liberan calor; las reacciones endotérmicas lo absorben. La energía total se conserva.
Ejemplo: Quemar madera es exotérmico — libera calor y luz. Una bolsa fría es endotérmica — absorbe calor y se siente fría.
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