Physical changes and changes of state Transitional Reasoning Practice

Questions

1. 1.

   A student places 15.0 g of crushed dry ice ($\text{CO}_2(\text{s})$) into a flask, quickly seals an elastic balloon over the flask opening, and measures a total assembly mass of 142.5 g. After thirty minutes at room temperature, the solid has completely disappeared, the balloon has expanded, and the balance still reads exactly 142.5 g. When the flask is subsequently cooled in an ultra-cold bath, solid white crystals identical to the original dry ice reform on the glass walls. Based on these observations, which statement provides the correct scientific justification for classifying this process as a physical change?

   • A) The expansion occurs because the covalent bonds within the carbon dioxide molecules break, releasing thermal energy to inflate the balloon.
   • B) The transformation represents a chemical change because the generation of a gas from a solid necessarily proves that a new substance has formed.
   • C) The molecular identity and total mass remained constant, with the transition altering only the intermolecular spacing and particle motion.
   • D) The transition chemically alters the carbon dioxide into an unstable gaseous element that can only condense under synthetic conditions.

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