Sodium nitrate dissolves endothermically in water: the measured overall standard enthalpy change is +20 kJ mol⁻¹, while the overall standard entropy change is +145 J mol⁻¹ K⁻¹.
Respond to the prompts below. No calculations are required beyond simple qualitative comparisons.
(a) Explain how the dissolution can be spontaneous at room temperature even though the enthalpy change is positive.
(b) Predict qualitatively how lowering the temperature to −10 °C would affect the spontaneity of the dissolution. Justify your prediction using the signs and relative magnitudes of the enthalpy and entropy changes.