Four separate transformations are carried out on macroscopic samples in a laboratory
CHEMISTRY · Multi-part · AP · Chemistry · Chemical Reactions · Chemical Reactions
Problem
Four separate transformations are carried out on macroscopic samples in a laboratory. Each transformation is described below. For every transformation, a student must decide whether the change that occurs is best classified as physical or chemical.
Transformation 1
A dark-violet crystal of iodine is gently warmed in a sealed, dry test tube. A visible purple vapor forms above the solid. After the test tube cools to room temperature, shiny iodine crystals are observed on the inner wall near the mouth of the tube.
Transformation 2
A strip of magnesium ribbon is ignited in air. After complete reaction, a white powder remains that has a greater mass than the initial ribbon.
Transformation 3
Liquid ethanol is added to liquid water at 25 °C. The temperature of the mixture changes by less than 0.1 °C, and no bubbles or precipitate are observed. After mixing, a single homogeneous liquid phase remains.
Transformation 4
Granulated zinc is added to 1.0 M aqueous hydrochloric acid at 25 °C. Bubbles immediately evolve from the surface of the zinc, and the zinc gradually disappears.
Use particulate-level reasoning to justify the most appropriate classification (physical or chemical) for each transformation.
(1) For each transformation (1–4), indicate whether the change is best described as physical or chemical.
(2) For each transformation, cite specific particulate-level evidence—such as the making or breaking of intramolecular bonds, formation or disruption of intermolecular interactions, or changes in the identities of the chemical species present—that supports your classification in part (a).
(3) Some textbooks describe dissolution of substances as a purely physical process. Compare Transformation 3 with Transformation 4 to evaluate this generalization. Support your argument with evidence from intermolecular and/or intramolecular interactions present before and after each transformation.