Why does the solubility of phenols increase with increasing temperature?
And what is the general trend with state and solubility?
Thanks guys :)
And what is the general trend with state and solubility?
Thanks guys :)
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"In accordance with Le Chatelier's Principle, when the dissolution process is endothermic (heat is absorbed), solubility increases with rising temperature, but when the process is exothermic (heat is released) solubility decreases with rising temperature."
Apparently pure phenols and pure water are in a lower energy state than a solution of the two, so dissolving phenols in water absorbs heat (i.e. converts kinetic energy of the molecules into potential energy) as the water and phenol molecules are pulled in the opposite direction of the water-water attractive forces (es.g. dipole-dipole and hydrogen bonds) and the phenol-phenol attractive forces (e.g. van-der-waal's attraction), and these forces are replaced by water-phenol attractive forces. It's unsurprising that these forces are weaker, as "like dissolves like;" phenols contain a benzene ring which is non-polar, and water forms very strong hydrogen bonds with other water molecules.
The reason that they will mix even though this puts them in a higher energy state is because the increase in entropy outweighs the increase in potential energy between the molecules. Thus the Gibbs free energy of the system is decreased even though the enthalpy is increased ( G = H - ST where G is Gibbs free energy, H is enthalpy, S is entropy, and T is temperature... S goes up so G goes down, even though H also went up a little bit).
The salts of phenol are more soluble because a) the salt is more polar than just the phenol, and b) they produce ions. Both make the phenol interact more strongly with water, which is very polar.
Apparently pure phenols and pure water are in a lower energy state than a solution of the two, so dissolving phenols in water absorbs heat (i.e. converts kinetic energy of the molecules into potential energy) as the water and phenol molecules are pulled in the opposite direction of the water-water attractive forces (es.g. dipole-dipole and hydrogen bonds) and the phenol-phenol attractive forces (e.g. van-der-waal's attraction), and these forces are replaced by water-phenol attractive forces. It's unsurprising that these forces are weaker, as "like dissolves like;" phenols contain a benzene ring which is non-polar, and water forms very strong hydrogen bonds with other water molecules.
The reason that they will mix even though this puts them in a higher energy state is because the increase in entropy outweighs the increase in potential energy between the molecules. Thus the Gibbs free energy of the system is decreased even though the enthalpy is increased ( G = H - ST where G is Gibbs free energy, H is enthalpy, S is entropy, and T is temperature... S goes up so G goes down, even though H also went up a little bit).
The salts of phenol are more soluble because a) the salt is more polar than just the phenol, and b) they produce ions. Both make the phenol interact more strongly with water, which is very polar.