[confusedstud]

Some ionic compounds melt before decomposing. However, why would that happen? When sodium carbonate melts, some of its ionic bonds are broken in the process but when left to cool it solidifies again. Then after melting it and heating it further, it will decompose. Is the explanation for this is that the activation energy of the reaction is greater than the amount of energy required to melt it? So it has to melt first before being able to decompose? While for substances that only decompose, the reason for it is that its activation energy is lower than its 'melting point' hence, it only decomposes instead of melting.

Thanks.

[Dan]

Is the explanation for this is that the activation energy of the reaction is greater than the amount of energy required to melt it? So it has to melt first before being able to decompose? While for substances that only decompose, the reason for it is that its activation energy is lower than its 'melting point' hence, it only decomposes instead of melting.

Sounds good to me.

[shalikadm]

that's why we use steam distillation for essential oils..It helps to lower the boiling point to let it evaporate before decomposition.

Steam distillation is a special type of distillation (a separation process) for temperature sensitive materials like natural aromatic compounds.

Many organic compounds tend to decompose at high sustained temperatures. Separation by normal distillation would then not be an option, so water or steam is introduced into the distillation apparatus. By adding water or steam, the boiling points of the compounds are depressed, allowing them to evaporate at lower temperatures, preferably below the temperatures at which the deterioration of the material becomes appreciable. If the substances to be distilled are very sensitive to heat, steam distillation can also be combined with vacuum distillation. After distillation the vapors are condensed as usual, usually yielding a two-phase system of water and the organic compounds, allowing for simple separation.

[fledarmus]

Yes, if the activation energy required for the molecule to react is lower than the energy required to break down the crystal lattice, then the molecule will react at a lower temperature than it will melt and is said to decompose rather than melt. If the activation energy required for the molecule to react is lower than the energy required to vaporize the compound, then it is said to decompose rather than boil.

[confusedstud]

Thanks for clarrifying this with me!