Chemistry Regents Exam August 2022
22. A chemical reaction occurs when
(1) H2O(g) forms H2O(l)
(2) H2O(l) forms H2O(s)
(3) O2(l) forms O2(s)
(4) O2(g) forms O3(g)
Explanation: A chemical reaction occurs when the identity of a substance changes. Let's look at the answer choices. In choice 1, we have gaseous water being converted to liquid water. The identity does not change since it is still water, just in a different phase. Same goes for choices 2 and 3. In the answer choice 4, oxygen gas O2 creates ozone O3. The identity of the substance changes and this must be our chemical reaction.
Answer: 4