A differential scanning calorimetry (DSC) experiment is performed on a 2.50g sample of compound X (molar mass 160gmol−1). The DSC trace shows two distinct peaks as the temperature is ramped from 150∘C to 300∘C under 1 atm pressure:
• An endothermic peak centered at 200∘C corresponding to an energy absorption of 50Jg−1.
• An exothermic peak centered at 240∘C corresponding to an energy release of 350Jg−1.
Subsequent analysis of the solid residue indicates the formation of a new compound Y, while the gas phase contains only undecomposed X. Assume that the baseline heat capacity has been subtracted from the DSC data.
(a) Convert the energy associated with each DSC peak to units of kJmol−1 for compound X.
(b) Based solely on the energetic data and the qualitative information about the residue, identify which peak corresponds to a physical change and which corresponds to a chemical change. Provide a complete justification that cites both energy magnitude and compositional evidence.
(c) Design an additional calorimetric or spectroscopic experiment that would allow you to confirm the classification made in part (b). Outline the key steps and the type of data you would collect, specifying how the results would support or refute your classification.
(d) Predict qualitatively how the energies of the two peaks would change if the experiment were repeated under a pressure of 5 atm instead of 1 atm. Explain your reasoning.