While preparing dinner, a student makes the following observations:
I. Water from the freezer warms from −5 °C to 0 °C and turns into liquid water.
II. A mixture of sugar and water is heated; the liquid darkens, bubbles vigorously, and emits a caramel odor.
III. Butter melts in a pan and later resolidifies upon cooling with no change in color or odor.
IV. A steel wool pad left near the sink overnight develops reddish-brown spotting.
Answer parts (a)–(d) regarding these observations.
(a) For each observation I–IV, classify the change as physical or chemical and cite specific macroscopic evidence that supports your classification.
(b) Choose one of the changes you classified as chemical. Describe, in terms of the particles present, what is happening to the composition and bonding of the substance(s).
(c) Choose one of the changes you classified as physical. Describe, at the particle level, how the arrangement and motion of particles differ between the initial and final states.
(d) For each change, propose a practical laboratory or household method that could reverse the change. Indicate whether your proposed reversal is realistically achievable and explain why.