a chemical change
As a compound
An element occur in nature as a pure element or as a compound.
Element
When you mix an element with a compound, a chemical reaction may occur. The element may react with the compound to form a new compound or may remain unchanged depending on the reactivity of the elements involved.
That's because of the way "compound" is defined. If atoms of an element combine with other atoms of the SAME element, then it's not called a "compound".
Cobalt, the transition metal, is an element. It's element number 27, and it does not occur naturally as an element or as a mixture, but rather as a compound. Links are provided.
Rearranged
When one element replaces another element in a compound during a chemical reaction
When a compound is mixed with an element. KCl is more than one element put together, thus it is a compound. Sodium (Na) is an element, so if you combine the two, it is a single replacement reaction.
When energy is removed from a gas, condensation occurs. When energy is removed from a liquid, freezing occurs.
During a single-displacement reaction, one element replaces another in a compound. This reaction is most likely to occur if a more reactive element displaces a less reactive element in the compound. The displacement reaction will result in the formation of a new compound and a free element.
One element takes the place of another in a compound.