Physical transforms are restricted to changes that result in a distinction in display screen without transforming the composition. (source)

e.g. Melting water or dissolving sugar in water

Chemical reactions room the processes by which chemicals interact to kind new with different compositions. (source)

e.g. Burning $ceH2$ come $ceH2O$

But what is dissolve salt in water? Is that a physical adjust (like dissolve sugar) or is the a reaction?


I would think that dissolving a non-reactive salt, like $ceNaCl$ in water can be considered as a physics change. This is because, you deserve to recover the salt by evaporating the water away.

From the Wikipedia page of physics change

In general a physical readjust is reversible making use of physical means. For example, salt liquified in water deserve to be recovered by enabling the water come evaporate.

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But the difference between physical and chemical change can be misleading and confusing in ~ times. In general, anything that does not readjust the constitution of the substance, is a physics change.

When friend dissolve $ceNH3$ in water, the following equilibrium is collection up:

$$ceNH3 + H2O NH4+ + OH-$$

But if you heat the water up, you will certainly get back the initial ammonia without any type of chemical adjust in the composition. However, the ammonia does change its chemical composition in water, as $ceNH4+$ ions room formed. By the argument, you can say that the resolution of one ionizable salt is a change.

In part cases, dissolution of a compound deserve to be referred to as a true chemical reaction. For example, as soon as you dissolve Calcium oxide ($ceCaO$) in water, a vigorous chemical reaction take away place, developing $ceCa(OH)2$. You cannot get back the original $ceCaO$ by simply evaporating the water. In instance of aqueous systems of $ceAlCl3$, if you shot to evaporate the water by heating the solution, you will certainly get back only $ceAl(OH)3$ together anhydrous $ceAlCl3$ reacts v water as soon as that is in contact with water, to form $ceAl6Cl3$.

What i am trying come say is that some alters can be classified into one of these types, while some other alters can not be offered a clear classification. Melting of water is clearly a physics change, when reaction that $ceH2$ and $ceO2$ is plainly a change. One another fact, putting repaint on a canvas is not always a physics change. In truth some paints are produced in such a method that during drying, part chemical reaction occur, as result of which the paint fixes steady on the surface. This is the reason plenty of water thinnable paints have the right to not be dissolved in water as soon as they end up being dry.

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To conclude, you have to not hold tough classifications favor that in her mind. However, my final verdict: dissolving a salt is physical adjust (mostly).