溫度高的物質經由熱傳導、熱輻射或熱對流將物質的熱能傳向溫度低的物質，放熱後有可能改變物質的性質（例如水的三態變化）又或者使其溫度升高，這個過程就稱為放熱過程。
 | 此條目需要擴充。 (2017年11月9日) |
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