Chemical change refers to a process in which substances [materials] undergo a transformation, resulting in the formation of new substances. This change is usually accompanied by a release or absorption of energy. Examples include rusting of iron [when iron reacts with oxygen in the air and forms reddish-brown rust], burning of wood [when wood combines with oxygen and produces heat and light], and baking a cake [when ingredients such as flour, sugar, and oil react together under heat to form a solid cake].
Very Simple Definition:
Chemical change is when things change to become something new. For example, when iron gets rusty, it becomes a reddish-brown color, or when we bake a cake, the ingredients mix together to make a delicious treat.