Question

when water freezes, it changes to ice. is this a chemical reaction? why or why not?
how can you tell whether a change in matter is caused by a chemical reaction?
link to article:
https://flexbooks.ck12.org/cbook/ck-12-middle-
school-physical-science-flexbook-2.0/section/5.
15/primary/lesson/recognizing-chemical-reactio-
ns-ms-ps.

Explanation:

When water freezes to ice, it undergoes a physical change. In a physical change, the substance's chemical composition remains the same. Water (\(H_2O\)) as a liquid and ice (\(H_2O\)) as a solid have the same chemical formula. A chemical reaction would involve the formation of new substances with different chemical formulas. To determine if a change is caused by a chemical reaction, look for signs such as the production of gas, formation of a precipitate, color change (in some non - physical cases), or a significant energy change (other than just phase change energy). If new substances are formed (identified by chemical analysis or by observing properties that are distinct from the reactants), then it is a chemical reaction.

Answer:

When water freezes to ice, it is not a chemical reaction. Because the chemical composition (\(H_2O\)) remains unchanged. To tell if a change is caused by a chemical reaction, look for new substances formed (e.g., through gas production, precipitate formation, etc., which indicate a change in chemical composition).