CHEMISTRY · Single correct · AP · Chemistry · Chemical Reactions · Chemical Reactions
Problem
Solid acetic acid is added to water. The temperature of the mixture changes negligibly, but the electrical conductivity of the solution increases to a moderate level. Which statement best justifies classifying the overall process as involving both physical and chemical changes?
(a) Because the temperature of the mixture does not rise, no bonds are formed or broken; the observed conductivity is due only to water’s self-ionization, so the change is purely physical.
(b) Dissolution disrupts hydrogen bonding between acetic acid molecules (physical), and partial ionization produces acetate and hydronium ions by forming a new O–H bond in H3O+ (chemical).
(c) Acetic acid dissociates completely into acetate and hydronium ions, producing new species; because the change is entirely chemical, there is no distinct physical aspect.
(d) Hydrogen bonds that form between water and acetic-acid molecules count as new chemical bonds, so the process is chemical only rather than physical.