For ammonia (NH3. ), the enthalpy of fusion is 5.65 kJ / mol and the entropy of fusion is 28.9

step 1 So for ammonia, the enthalpy of fusion is 5 .65 kilojoules per mole, and the entropy of fusion i

For ammonia (NH3. ), the enthalpy of fusion is 5.65 kJ /...

For ammonia $\left(\mathrm{NH}_{3}\right.$ ), the enthalpy of fusion is $5.65 \mathrm{~kJ} / \mathrm{mol}$ and the entropy of fusion is $28.9 \mathrm{~J} / \mathrm{K} \cdot \mathrm{mol}$. a. Will $\mathrm{NH}_{3}(s)$ spontaneously melt at $200 . \mathrm{K}$ ? b. What is the approximate melting point of ammonia?

For ammonia $\left(\mathrm{NH}_{3}\right.$ ), the enthalpy of fusion is $5.65 \mathrm{~kJ} / \mathrm{mol}$ and the entropy of fusion is $28.9 \mathrm{~J} / \mathrm{K} \cdot \mathrm{mol}$.
a. Will $\mathrm{NH}_{3}(s)$ spontaneously melt at $200 . \mathrm{K}$ ?
b. What is the approximate melting point of ammonia?

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Key Concepts

Entropy of Fusion

The entropy of fusion (?S_fusion) represents the change in disorder or randomness when a substance melts. During the transition from a structured solid to a more disordered liquid, the entropy increases, and this increase is a driving force for the melting process, particularly at higher temperatures.

Enthalpy of Fusion

The enthalpy of fusion (?H_fusion) is the amount of heat energy required, per mole, to change a substance from the solid phase to the liquid phase at its melting point. It reflects the strength of the intermolecular forces that must be overcome during the phase change.

Gibbs Free Energy

Gibbs free energy (?G) is a thermodynamic potential that determines the spontaneity of a process. For any process, if ?G is negative the process is spontaneous; if it is positive, the process is non-spontaneous; and if it is zero, the system is at equilibrium. In phase transitions, the expression ?G = ?H - T?S is used to link the enthalpy change, entropy change, and temperature.

Phase Transition and Melting Point

A melting point is the temperature at which a substance transitions from a solid to a liquid phase under equilibrium conditions (?G = 0). At this temperature, the energy provided by thermal motion is just sufficient to overcome the lattice energy of the solid, making the liquid phase thermodynamically favorable.

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