Which process is a chemical change?

NY Regents Chemistry Exam June 2022

18. Which process is a chemical change? (1) condensation of H2O(g)

(2) synthesis of MgO(s) (3) evaporation of C2H5OH(l)

(4) sublimation of CO2(s)

Explanation: A chemical change occurs when the identity of substance changes which happens during a reaction. We have to identify which of the following answer choices represents a reaction. Phase changes are not reactions. Thus, 1,3 and 4 can be eliminated, leaving us with choice 2

Answer: 2