## Chemistry and Chemical Reactivity (9th Edition)

a) Change in the state of matter (solid to gaseous) is a physical change. b) Molecules occupy more space as their average energy increases: physical change. c) Combustion reaction converts methane and oxygen into carbon dioxide and water vapor, releasing heat: chemical reaction implies chemical change. d) NaCl is an ionic compound, when dissolved in water It breaks into íons ($Na^+$ and $Cl^-$), which is a chemical change.