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Signs of ΔH and ΔS: physisorption, diamond to graphite, protein denaturation and propene to cyclopropane

Four processes, measured one after another on a virtual bench. N2 molecules stick to charcoal while an adsorption calorimeter reads the heat and the Sackur-Tetrode entropies of a 3-D gas and a 2-D film give ΔS; a diamond lattice opens into graphite sheets while a Hess ladder built from two combustion enthalpies gives ΔH; a protein unfolds in a DSC cell while the endothermic peak is integrated for ΔH and ΔS = ΔH/Tm; propene closes into cyclopropane while a second Hess ladder and third-law entropies give its signs. Sign meters swing for each value, every process lands on a ΔH-ΔS sign plane, List-II is matched and options A-D are tested entry by entry. No prediction stage - input, run, watch, result.

Sub-topics covered

• Enthalpy change and heat flow at constant pressure
• Entropy change and molecular freedom
• Hess's law from combustion enthalpies
• Physisorption thermodynamics
• Protein denaturation (two-state model, DSC)
• Ring strain in cyclopropane
• Gibbs energy and spontaneity

What it teaches

• Physisorption: a van der Waals attraction forms, so heat is released (ΔH < 0); a 3-D gas becomes a 2-D film, so ΔS < 0 - entry (2)
• Diamond to graphite: ΔH = ΔcH(diamond) - ΔcH(graphite) = -1.9 kJ/mol; S(graphite) > S(diamond), ΔS = +3.36 J/K mol - entry (5)
• Protein denaturation: hydrogen bonds break (ΔH > 0); the unfolded chain has many more conformations (ΔS > 0) - entry (1)
• Propene to cyclopropane: ring strain makes ΔH = +33.3 kJ/mol; closing the ring freezes the CH3 rotor, ΔS = -29.5 J/K mol - entry (4)
• Only option C (P2, Q5, R1, S4) matches all four; (3) ΔS = 0 fits none of the processes

Simulation ID

• ADV-2026-P1-CHE-Q13 · revision 1

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