A chemical change, or chemical reaction, is a process in which one or more substances are converted into different substances with new chemical compositions. Because new substances form, a chemical change is usually accompanied by signs such as colour change, gas evolution, or heat release. The burning of wood is a chemical change, whereas the melting of wax is only a physical change.

化学变化(化学反应)是一种或多种物质转化为具有新化学组成的不同物质的过程。由于生成了新物质,化学变化通常伴随颜色改变、气体放出或热量释放等现象。木材燃烧是化学变化,而蜡的熔化只是物理变化。