CHEMISTRY · Single correct · AP · Chemistry · Chemical Reactions · Chemical Reactions
Problem
Solid NaOH pellets are added to water at 25 °C. The pellets dissolve completely and the temperature of the solution rises noticeably. Which classification of this overall process is most appropriate, and why?
(a) Chemical change, because energy is released when NaOH reacts with water to form new substances.
(b) Physical change, because the ionic species present before and after the process are identical.
(c) Chemical change, because ionic bonds in the solid lattice are broken and new ion–dipole attractions form with water molecules.
(d) Both a chemical and a physical change, because dissolution is physical but the temperature rise is chemical evidence.