At 0C°, the freezing point of water, equilibrium between ice and water is made. At that temperature, neither the ice melts nor the water freezes, and neither direction is thermodynamically feasible. Also, there’s an equilibrium made when water reaches its boiling temperature.
At these melting and boiling points, where equilibrium is made, the value of ΔS° (total) is zero.
ΔS° (system) + (-ΔH /T) = 0
To calculate the temperature at which the reaction is at equilibrium:
T = ΔH / ΔS° (system)
The expression above explains why boiling and melting temperatures depend on the strength of the forces between the particles. As, the melting & boiling temperatures depend on the amount of energy required for the change of state.
Strong force = large amount of energy needed to separate the particles = high melting or boiling temperatures.
Note: The reactants are thermodynamically unstable relative to the products if ΔS° (total) for the change is positive. That means that the reaction is thermodynamically feasible.
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