A student measures the standard molar free energy change for the dissolution of Solid…

CHEMISTRY · Multi-part · A Level · Chemistry · Thermodynamics · Thermodynamics

Problem

A student measures the standard molar free energy change for the dissolution of Solid C at four temperatures. The results are tabulated below. Temperature (K) 280 300 320 340 ΔGdiss∘\Delta G^{\circ}_{\text{diss}} (kJ mol−1^{-1}) 4.80 3.40 1.90 0.40 Assume that the enthalpy and entropy changes for dissolution remain constant over this temperature range. (a) Using the data, determine numerical values for the standard molar enthalpy change and the standard molar entropy change for the dissolution of Solid C. Show your method clearly. (b) Calculate the temperature (to the nearest kelvin) at which the dissolution of Solid C becomes thermodynamically spontaneous under standard-state conditions. (c) At 360 K the experimentally determined ΔGdiss∘\Delta G^{\circ}_{\text{diss}} is found to be −0.90 kJ mol−1-0.90\,\text{kJ}\,\text{mol}^{-1}. Discuss whether the assumption of temperature-independent ΔH∘\Delta H^{\circ} and ΔS∘\Delta S^{\circ} is reasonable, supporting your argument with quantitative reasoning.

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